What game should I reverse engineer?
Seeing as you have experience creating material for ROBLOX, I would suggest any Source Engine game; seeing as ROBLOX and (most) Source Engine games are both based on Lua you should be less troubled to learn too much about the Source Engine before you start. Valve also doesn't seem to be too keen on creating a stable anti-cheat since they're capitalizing on banned players buying new accounts; it's pretty clear by the high traffic of uploads to the Counter-Strike: Global Offensive section here on M.P.G.H. that there is definitely a player base and interest in material for that game, but the competition is high in that specific title. If you're really strapped for cash, you should start with some of the free titles like Team Fortress 2, No More Room In Hell, etc.
I just found out about this game called "POKEONE", looks pretty new and it seems that their anticheat might not be the best right now knowing that the game is in it's open beta phase. You might want to consider looking into it and seeing what you can do.
Realm of the Mad God
Team Fortress 2
toribash or gta 5 =)

Did you get a gpu refund with dama/ have they appealed you pp dispute ?