Can I include casino-like games in mine? it'll be half the game and would like to know before setting off. I get if that's something we'd like to strive away from.

I found a list from when GTA released it's online casino (one way purchase, no withdrawal of actual cash or irl items). The list is provided from a reddit post here. I'd like mine to have 'not-cash' and be self contained in-game currency. 

Looking for a dev? I was wanting to create a card game as well.

It sounds fine if part of the game is earning game-cash to play in an in-game casino. Many games involve earning some kind of in-game currency to unlock progression.