Valentine's day for the Straw Hat's crew? Alrighty.

Also, I feel Robin should have been the School Teacher. Just seemed like it'd be more fitting to me.

If we're putting them in the same group, class/school president would be more fitting. She's(Robin) part of the group, but also monitors it. A teacher would be too disconnected from them.
Hancock would be the idol of the school.
Nami the slightly famous girl excelling in a certain subject/field.
Sanji the player that can't get his real targets, also an open pervert.
Usopp, the eternal liar and prankster.
Franky, the exhibitionist.
Zorro, the "who the fuck cares, I want food and fights" guy.
Tashigi his admirer.
Brooke, the... panties enthusiast
Chopper would be the mediator, after the bones are broken and the skin is torn.
Luffy, our male protagonist in everyday harem, who just have that particular appetite