The setup is fine since you're obviously trying to be budget conscience. I'd say cable management is really what you need more than anything else.

However, if you're handy with wood and a saw, or sheet metal and a brake (I assume you don't have a 3d printer):

• Stack them in sets of 4. The design of those NUCs allow them to be stacked without any thermal issues, as long as the ambient air is kept low enough.
• Put the power supplies for each stack at the bottom of the stack in a 2x2 pattern (two side by side and stacked 2 high) - they should then match the footprint of each NUC
• Set up a frame to hold each stack, I'd recommend 4 posts of 1/2"x2" flat stock wood (or 18GA steel strapping), 2 running along each side with 6"x6" platforms for each stack level to hold the frame together
• For stack platforms at a minimum I recommend one at the bottom to hold your termination points (see below), one about 1" above the bottom one for the power supplies, one separating the power supplies and NUCs, and if you're using sheet metal, one for each NUC. You can also add a cross bar at the top to use as a handle.
• For power, those DC bricks use a standard C13 connector, so I would recommend a short length 4xC13-to-1xC14 splitter so that you only have one C13 input for the entire stack of 4 NUCs (if you're in Asia, your local electronics shop should be able to make you a few splitters for pretty cheap if they don't already have ones kicking around)
• Both the NUCs and the DC bricks should be ziptied/string tied, or velco'ed to stack frame
• Route the single C14 input to the bottom of the stack to the termination level (will probably be about 6"
• Same for the network cables, run them down the side zip tied to frame and have them terminate at the bottom termination level. If you're decent at terminating, or if you know someone who is fast at it, you can just crimp custom length cables for each of the 4 NUCs. Otherwise it should be 2x12" cables and 2x18" cables.
• At the bottom I personally would recommend terminating with a CAT5e/CAT6 jack rather than a plug
• Then orient your termination points so they point forward, that way all the cable hide at the back of the stack

Once you have all your NUCs in modular stacks, you can just run network cables and C13 power cords neatly along the front of the shelf, and have them input at the bottom of each stack. Then just tie your runs to each stack in a neat bundle and mount your switches to the underside of those shelves.

If you need to service a stack, you can just disconnect the stack in question at the termination points at the bottom of the stack and lift the whole assembly out, without having to play with wires. If you want to be extra fancy, you can even set up grooves or guides on the shelf to ensure the stacks are always placed in the correct position.

This is the master reference thread for Lenovo Tiny https://forums.servethehome.com/index.php?threads/lenovo-thinkcentre-thinkstation-tiny-project-tinyminimicro-reference-thread.34925/

Patrick has alot of other writeups on the STH main site.

Personally my preference is Lenovo P330 or M720q:

• Supports x8 PCIe 3.0 low profile card or a 2.5" SATA drive
• 1xM.2 for M720q; 2x M.2 for P330
• 2 DDR4 SODIMM slots
• 2x 10G USB3.2 ports
• 1xM.2 B key supports non-wifi cards also (e.g. Zigbee/zwave)
• Heatsink technically supports up to 65w i9-9900 (though you leave alot of performance on the table for sustained workloads), but most come with an i5-8500T

There's also the HP T740 which also supports a PCIe card, but is a bit taller than 1U

You might be thinking of the Dev network keys (MSDN).

MSDN used to be free so this was a common approach, but they re-org'ed all their programs so I think those keys are now hiding under the paid MSDN program...

If you have a university that supports alumni, Microsoft grants a key to each student, faculty, and alumni in most of their post-secondary education plans.

My other recommended way is through the Startup Hub.