What's Bonney's role?
Cabin Girl; Questionable Ship Skills
Dream?
Follow Nika; When does the dream end?
Another "Big Eater" in the crew seems redundant being that's a defining trait for Luffy. Though that trait would fit Luffy's apprentice...
Her joining would make her the youngest...though Chobro has experience being the older one.
Support Mage.
One Piece makes more sense if you look at it like an RPG, and give the characters actual classes.
This makes sense since One Piece's original villains, the Shichibukai, were modeled after an old RPG Oda played as a kid. On some levels, One Piece is an RPG in Manga format.
Luffy = Monk/Hero (hence Luffy being a saint/savior/God. Monk-ey D. Luffy)
Zoro = Swordsman/Warrior
Nami = Mage/Thief (elemental/weather based)
Usopp = Ranger/Bard (storyteller)
Sanji = Monk/Cleric (foot based combat, heals through food)
Chopper = Cleric/Warrior
Robin = Mage/Ranger (transmutation based, can use powers to spy and attack from long range)
Franky = Sailor/Mechanic
Brook = Bard/Swordsman
Jinbei = Warrior/Sailor
Vivi = Diplomat/Warrior
Karoo = Beast/Vehicle
Yamato = Warrior/Hero
Carrot = Scout/Warrior
Tama = Beast Tamer/Ninja
Momo = Beast/Warrior
Boney would be a Mage/Warrior who fights, but also enchants her allies with aging buffs and attacks the enemy with ageing debuffs.