Luffy - He needs to improve his base stats. They are ridiculously low, especially the AP. And he must improve his resistance with the G5.
COA level should also improve.
Zoro - He is the strongest by far. Maybe it will only slightly improve its mobility over long distances, nothing more for now.
Sanji - More AP, resistance, DC, defense, improve COA, COO, and learn ranged attacks. But especially, Sanji should improve the COA in a beastly way.
Jimbe - COO, speed, mobility, DC. dexterity.
Franky - COA, COO, speed, mobility, defense, CQC, agility, dexterity,
hand-to-hand skills and techniques
Brook - Resistance, AP, defense, durability, COA, COO, DC, range attacks.
Robin - Resistance, defense, durability, COA, COO, skills.
Chopper - AP, COA, COO, skills, dexterity, DC, medical skills.
Nami, usopp - LOL