Got sent a data dump for the game. Seems there's IVs (Individual Values, sort of akin to genetics if you're not aware of standard Pokémon fare) in the game, there is a max CP level for each Pokémon.
You can only go up to an absolute maximum of 40 "levels" of a Pokémon (but most will be a lot less since they start higher).
STAB is in the game at *1.2 rather than the main game's *1.5, so if you have a Pokémon with a move that matches its type, it's definitely a better option to use for a gym battle.
Currently trying to properly decode the data and will put some full lists up on my site at some point. The systems are surprisingly complex considering how simple the gameplay is.