I am a complete noob to backups and NAS', so pardon my newbie question

I want to run my own Dropbox/GDrive-like box, because I don't want to pay these companies a subscription just to store my files, at a high price, with no privacy.

I have terabytes of photography, due to being a hobbyist street photographer where each photo is over 50 megapixels, so 100 MB+ per photo. I am quickly running out of space in my computer despite my terabyte SSDs. So I am trying to think of a more scaleable way to do this on my own.

I was thinking of getting a NAS from Synology or TerraMaster, and put 2x 20 TB HDD drives in there in RAID 1, because I am filling up my storage FAST. Or maybe I would get a 4 drive bay NAS so I can do RAID 10.. I am not entirely sure -- this sounds more expensive.

Some requirements:

• I want to be able to access my RAW photos from anywhere
• I want to be able to sync my Lightroom Catalog between my Mac (when I travel) and Windows (my primary PC)
• I want to make sure my photos are properly backed up, redundantly in case a drive fails
• Secure & private
• A bonus is performance, but with HDD drives, I know I won't be getting the performance as if I have everything in a built-in NVME or SSD, which I have right now. However, I don't mind having some files local to the NVME from recent shoots, and then moving stuff over for long term storage

I am a complete nub to this, so I have some questions:

1. Is a NAS the best solution for this?

2. Should I go for a 2x drive bay, or more?

3. Is there perfomance degradations if I am at home where the NAS and desktop/laptop are in the same network?

4. Are there any other questions I should be asking but haven't asked?