I know theres only a few palettes to use in overworlds, and its too late for me to apply JPAN's engine, so which palettes can I use? Just the overworld (people ones?)
The ones that work in game. Those you can use:p.
Well, cheats (I'll assume GameShark or AR type) work by "hooking" into the ram and then altering it. So, in order to prevent cheating, you would need to use ASM and rewirte all of the RAM storage to shift it around. This would be quite difficult. My advice is to put something at stake for cheating. Like anyone caught cheating has to pay each of the other guys $20. Cheating is fairly easy to note, excessive shinies, high stats, more than one of a single legendary, more than one master ball, and pokemon not found in FR. So, I would say put up a little punishment for cheating and hope you can trust them:p.