I think you can get by without crafting, and rely upon gathering and selling your collected materials.
Materia can be acquired yourself, by breaking down 100% spiritbonded items.
Not sure about buying, since I am new myself and havent really dabbled in this yet.
But i assume this is possible to just grab from the marketboard.

As far as your levelling question; I guess this is up to taste really.
Whatever you like to focus on, since both are levelled independantly.