Just a few thoughts:
There might be people running MorphOS on as low as 1024x768, which should be quite sufficient for a game like Chaos???.
You should allow users to select a different (bigger) screenmode and center your game to it (if you don't want to scale it up) this would allow users to enjoy the game on 16:10 or 16:9 displays without f###ing up the aspect-ratio of your GFX.
It might also be nice to have the game running windowed on the Ambient screen.
68k-binary should be fine for the moment.
My Efika runs 800x600 only (the 10" display). But I think that's not very common and probably should not be considered (I a have enough alternative higher resolution systems to use anyway).
