You can spend the remaining SP however you like
Matching elemental weakness isn't a big deal with how overcharged your Lightning and Ice techs are on this build
The only thing you're gonna need to learn is how to do positioning for the stances and how to utilize Tech Arts. Extra Chaser Damage is just for a slight boost against some enemies. Additionally make a PP conversion (R) Ring to get a temporary PP recovery boost. Your best friend is gonna be Gizonde but try experimenting a little yourself too.