Thank you for your reply! I did a bit of research and, since I do want to use quite some peripherals, I have gone for the ULX3S. A big factor here was documentation and availability; If I would have been able to find a MiSTer Pi I might have gone for that instead.

I now bought a ULX3S on a whim, and will at least evaluate how usable it is for my purposes. It will take quite some time to familiarize myself with a new toolchain, which kinda sucks. One advantage of these big proprietary IDEs is that they integrate a lot of functionality into one "unit" (as far as the user/programmer is concerned), instead of having to install a lot of separate tools.

For the course, I am now considering to "support" an AMD board, an Intel one, and a Lattice one.