Instead of materias give +1 +2 +3 +4 resistance of certain element how about these materias give a percentage like 1% for materia I - 4% to materia IV? I was thinking in give a cap of 15~20% of resistance too.
About the twelve we can do things like Thaliak will give +2% resistence of water, for example.
Status and Physical resistence could work in the same way, but with a cap of 10% to physical and 40%~50% to status