The development thread is here. The engine is polygon-based so it doesn't actually take 3D skills to make levels. You do have to have some decent sense of architectural aesthetics though, obviously.

I'm still not 100% sure what I need, but custom graphics would be nice for obvious reasons. I have a race of aliens that I've just made into "shapeshifters" right now, but given the way the engine is programmed it's not actually possible to make them shift shape (though if I learn Lua well enough it probably would), so it would probably be better just to give them their own appearance.

Apart from that I really would like to give each environment its own unique appearance (it takes place on a number of different planets, most of which have never been seen before in the series' history) so someone who can create textures would be greatly appreciated.

Beyond that there's probably other things that could be done but I haven't thought about all of them yet.

It would be cool if you'd contribute; I'd welcome it.