The actual main stat for an RDM is Intelligence. Unlike a melee RDM weapons attacks are infused with magic, higher your magic better your damage. Its also a good idea to add Strength Materia for your auto hit in between the casting. It won't be much but an extra 2-300 hit will add up.
RDMs naturally crid hit so you don't need to really worry about that, i've only not crid hit maybe once or twice a week.