Hi there! If you're aiming to emulate 8/16 bits games on a PC platform, I think that you can get inspired by GB/GBA/SNES and SEGA emulators and how they set buttons around the keyboard. Most of these emulators set the movement buttons on the arrow keys, and action buttons goes to the left corner of the keyboard (ZX/ASZX/ASDZXC for example).
And of course, try some games on them so you can get inspired on gameplay elements.
Like Contra
A personal favorite of mine is Sunset Riders, but is set on the Far West instead of a SciFi context.
I hope this helps a bit. Cheers!