In true Sakurai fashion, I'll be leaking information about the RPG update by update until it's ready.
Each player character will have a Combat Class and a Character Class.
A Combat Class describes what type of weapon the character carries.
Buster: Low power, high accuracy, medium defense
Bomb: High power, low accuracy, medium defense
Sword: Medium power, medium accuracy, low defense
This doesn't mean that this is all you can use, though. Just choose whatever is closest to what you want to use. Weapons like ZX-style energy guns fall into the Buster Class, most projectiles into the Bomb Class, and so forth.
Gotta wrap this up here, thunderstorm.