Stable Diffusion 2 base model is trained using what we would today refer to as a "censored" dataset. Stable Diffusion 1 dataset included NSFW images, the base model doesn't seem particularly biased towards or away from them and can be further trained in either direction as it has the foundational understanding of what those things are.
You are correct, page 10 does say that the hook point should meet 1/8 inch above the needle eye, at the bottom of the needle's stroke.
Missing stitches only when the fabric is in place suggests that your thread tension may be too high. Check the top thread tension, make sure that you can pull the thread through with only a slight pull at the "0" position (check page 9 of the service manual).
This sounds like a timing issue to me. The thread bunching up may be due to the hook not grabbing the thread or the take-up lever not taking up the slack at the correct time. If it's missing stitches in zig-zag mode then that would also be due to either hook timing or possibly needle bar alignment.
Simple things to check:
Make sure that the needle is installed correctly, especially that it is oriented the right way and inserted all the way in
Make sure that the take-up lever is threaded correctly
Assuming these are both correct, you can try the following:
If possible, insert a fresh needle (at least, you will need a needle that is undamaged and not bent from the shank up to the eye)
Remove the plate, leave the machine unthreaded
On the straight stitch setting, turn the hand wheel slowly and check that the eye of the needle is exactly level with the hook as they pass each other (this should happen close to the bottom of the needle's stroke but may not be exactly at the bottom)
On the widest zig-zag stitch setting, again turn the hand wheel slowly and check that the eye of the needle passes closely to the hook (it won't be exact because the needle has moved, but it should be just slightly early on one side and just slightly late on the other, not noticeably early or late on one side) and also check that the needle is not colliding with any solid parts of the machine on either side
If the eye and the hook are not aligned as they pass each other, then you have either a timing or a needle height alignment issue. If they pass correctly on the straight stitch but the needle is noticeably early or late on one side of the zig-zag stitch (and fine on the other side) then you have an issue with the horizontal alignment of the zig-zag stitch.
That machine is a pretty solid choice if it works, and a worthwhile repair project if it doesn't (it may have seized up if not maintained recently or it may have timing or alignment issues from age).
Machines like that are quite solidly built compared to modern machines, I would be surprised if it can't get through a few layers of denim for a few stitches (I wouldn't recommend doing 6 layers continuously, but crossing over the side seam should be OK). If you're concerned you can always hand crank it for that part.
The lack of a free arm may be somewhat limiting for hems. The "stupid" solution would be to stand the machine up on top of a crate or similar, as long as the circumference of the leg/other fabric is large enough to fit around the bottom metal "plate" of the machine. (These machines have a metal body designed to be built into a cabinet or shelf top. I'm not sure if yours includes a wooden box around the bottom or if it is just the machine itself, but if there is any wood then the machine can be removed from this leaving just the metal body of the machine itself which may provide more flexibility in this regard.)
I haven't come across any significant discussion surrounding this before and I wouldn't recommend choosing a machine on this basis.
A front-loading bobbin is only an advantage for changing mid-task if you catch it before the thread runs out, otherwise you'll be backtracking and starting again anyway once you've replaced it. I suppose if there is a viewing window and you can see when it is about to run out then this is an advantage, otherwise you won't know when to stop and change it anyway until you notice that it has already run out.
In terms of speed I doubt you will find any typical sewing machine "too slow" unless you plan to sew a lot and you want it finished quickly. For a few repairs or alterations and the occasional custom piece speed is not a priority, most of the time you will want to go slower anyway for more control/accuracy.
I think you need to put less thought into what machine you get and more thought into getting some machine and start sewing without thinking so much about details like how the bobbin is loaded. As a beginner these things don't matter, and by the time you are non-beginner enough for them to matter then you will know what aspects are important to you and if you want to upgrade. As it is, you can't really jump to making "expert-level" choices because you don't have the experience to know, for example, if speed is even a priority to you.
So... If this doesn't actually increase the context window or otherwise increase the amount of text that the LLM is actually able to see/process, then how is it fundamentally different to just "manually" truncating the input to fit in the context size like everyone's already been doing?
Singer are by far the best for finding replacement parts and repair guides, followed somewhat by Brother. I would recommend avoiding the others if you want to be able to maintain or repair the machine in the future.
The stitch patterns should be documented in the manual. Otherwise they are somewhat self explanatory. The symbol looks somewhat like how the stitch will look. Straight stitch is usually a straight line (possibly dashed or dotted), and is usually the first pattern listed. Zigzag stitch looks like a line that moves from side to side in evenly-spaced triangles and is usually the second pattern.
There may also be various asymmetrical variations of the zigzag stitch, or ones that get narrower and wider over time, these are probably what you're referring to as "all the other symbols". Most of these will function as stretch stitches but you don't need to use or care about them unless you specifically want them for their appearance. They make no functional difference. Some of the more elaborate ones may not stretch evenly or adequately.
If the machine has a straight stretch stitch option (as I explained in my other comment) then the symbol for this may vary so check the manual. It's usually some sort of a straight line with dots or dashes.
Some machines also have a button hole mode which is usually listed alongside the other stitch options. Again the symbol for this can vary but it is usually some sort of a rectangle with wavy lines, and it is usually clearly marked in a different color or with a border around it or similar to distinguish it from the others.
Regarding needles, spools, etc.: Needles are completely standard and replaceable and interchangeable on all machines except antiques and this should be the first thing that you do anyway. You can get a twin needle for specific tasks but generally you won't need one, it is not "more useful" than having just a single needle (this is not a "two is better than one" situation). The most important thing to make sure that you have is the presser foot, there should be one attached to the machine and most machines are intended to include one or two other types that can be swapped out (e.g. a narrower one that is useful for particular types of fabric or for working in tight situations) and if these are missing then you will have to try to find replacements or do without as they are mostly NOT interchangeable between machines of different brands or families. Check the manual for what accessories should be included, and make sure to look for them in the accessories compartment. It would be useful if the machine included one or two bobbins so that you can get started sooner but these are mostly standard and easy to find online (there are a few different types so make sure you work out what type you need).
I would highly recommend watching a few beginner/introductory machine sewing tutorials so that you can learn about the various parts of the machine and how it is set up and used, even if you aren't planning on doing any actual sewing from scratch. This will make it a lot easier to know what you need and understand what you're looking at.
I actually like stuff that is simple and repairable. My sewing machine is electromechanical and has no computerised operation. These machines are also a lot cheaper to buy second-hand, of course.
The only stitch types that you actually need are a straight stitch and either a zigzag stitch or a stretch stitch. The zigzag stitch is what it sounds like, and can be used for seams that need to stretch. The stretch stitch involves making 2 forward stitches and 1 backwards stitch in turn, this also allows the seam to stretch and it looks neater because visually the stitch is in a straight line.
The other stitch types that you typically find on a home sewing machine are really only used for decoration and are not essential.
I tried getting it to write out a simple melody using MIDI note numbers once. I didn't think of asking it for LilyPond format, I couldn't think of a text-based format for music notation at the time.
It was able to produce a mostly accurate output for a few popular children's songs. It was also able to "improvise" a short blues riff (mostly keeping to the correct scale, and showing some awareness of/reference to common blues themes), and write an "answer" phrase (which was suitable and made musical sense) to a prompt phrase that I provided.
There are only a few popular LLM models. A few more if you count variations such as "uncensored" etc. Most of the others tend to not perform well or don't have much difference from the more popular ones.
I would think that the difference is likely for two reasons:
LLMs require more effort in curating the dataset for training. Whereas a Stable Diffusion model can be trained by grabbing a bunch of pictures of a particular subject or style and throwing them in a directory, an LLM requires careful gathering and reformatting of text. If you want an LLM to write dialog for a particular character, for example, you would need to try to find or write a lot of existing dialog for that character, which is generally harder than just searching for images on the internet.
LLMs are already more versatile. For example, most of the popular LLMs will already write dialog for a particular character (or at least attempt to) just by being given a description of the character and possibly a short snippet of sample dialog. Fine-tuning doesn't give any significant performance improvement in that regard. If you want the LLM to write in a specific style, such as Old English, it is usually sufficient to just instruct it to do so and perhaps prime the conversation with a sentence or two written in that style.
WizardLM 13B (I didn't notice any significant improvement with the 30B version), tends to be a bit confined to a standard output format at the expense of accuracy (e.g. it will always try to give both sides of an argument even if there isn't another side or the question isn't an argument at all) but is good for simple questions
LLaMa 2 13B (not the chat tuned version), this one takes some practice with prompting as it doesn't really understand conversation and won't know what it's supposed to do unless you make it clear from contextual clues, but it feels refreshing to use as the model is (as far as is practical) unbiased/uncensored so you don't get all the annoying lectures and stuff
IMO, local LLMs lack the capabilities or depth of understanding to be useful for most practical tasks (e.g. writing code, automation, language analysis). This will heavily skew any local LLM "usage statistics" further towards RP/storytelling (a significant proportion of which will always be NSFW in nature).