What is the maximum amount of ROM & RAM that you can put in a cart ?

The GB & GBC can only access 32K bytes ROM & 8K bytes cart RAM at one time. As a result, this is all you can access unless you use a Memory Bank Controller (MBC) or design something similar yourself that does the same function. The total amount of ROM or RAM accessible then becomes a function of the limitation of the MBC itself. Yon can have virtually unlimited ROM or RAM in a cart if you design your own MBC from scratch. If you use a Nintendo MBC, then here are the Nintendo MBC limits.