hello, I hope you can see the setup I have here. I posted earlier today but dont think it had my updated setup.
Im looking for advice on putting together a small setup I can connect to my keyboard to add spacey melodic sounds.
Im not sure what equipment to put in the case to make sure I have all the audio connections I would need for keyboard, headphone, and computer.
I also would like to know if Im missing some major components that I should add or replace in the case.

The case is going to be an immediate problem. While you could build something in 3U x 104 hp that would fulfill the basic needs here, you'll wind up with compromises due to the lack of space. The Maths, for example, takes up about 1/5th of the panel space...and when you have loads more to put in to result in a usable synth, that 20 hp chunk will probably wind up being a stumbling block.

Instead of this (assuming that the single 104 skiff is the "updated setup"), have a look at some cases that fix this problem. The Tiptop Mantis comes to mind right off, as does Intellijel's 7U x 104 case. Or if you want something beefier, see here: https://www.etsy.com/shop/CaseFromLake?ref=simple-shop-header-name&listing_id=687830767 and compare their prices vs. other similar cabs. I like what I see with them, plus I've not heard Complaint #1 about their work, and for what they're making, the prices are STOOPID-cheap!

Also, it's important to remember to do your initial MG builds with a "case" that's MUCH larger than you think you'll need...because, invariably, you'll think you need a smaller case than you actually DO. Work out a build that seems right, THEN pare it back to an available-to-buy size. Once you get this part sorted, THEN it'll be time to start examining possible builds.