You need only the AXS RD, Wireless Blips, and a 12-speed cassette with a matching chain. The latest AXS firmware no longer requires levers or a blip box.
3D-printed holders would be a good idea. I feel like leap components are the most used ones, but there are many options based on how your friend wants them set up.
I would go with a road RD. You won't have any issues with the jockey wheels and not using a flat top chain.
However, I suggest you use the SRAM cassettes. Their progression is excellent, and the 10 T is great as it moves most of your most used gears into the center of the block, so you get a nice chain line. You get those excellent 1T jumps where it matters, even with the 10-33. Also, the force and red chains last a long time and are worth the cost.