One costume per character would work. Let me try to pick one out for each characters on my latest roster.
Mario - Strikers Charged Mario
Luigi - Mr. L
Peach - Tennis Open Mario
Bowser - Dry Bowser
Bowser Jr - Bandanna Wearing Bowser Jr
DK - Boxing Gloves DK
Diddy/Dixie - Sports Diddy/Dixie
Yoshi - Yarn Yoshi
Wario - Classic Wario
Villager - Female Villager
Link - Skyloft Link
Zelda/Impa - Priestess Zelda/Scarfed Impa
Ghirahim - 2nd Form Ghirahin
Toon Link - Conductor Toon Link
Ganondorf - Classic Ganon
Samus/ZSS - Classic Suit Samus/Other M Cadet Samus
Ridley - Prime 3 Skinned Ridley
Pit - Classic Pit Clothes
Palutena - Classic Pit Palutena
Little Mac - Pink Jogging Suit Little Mac
Kirby - Yarn Skinned Kirby
Metaknight - Unmasked Metaknight
King DeDeDe - Masked DeDeDe
Olimar - Olimar w/ Pikmin Suit Type Design
Matthew - Matthew w/ Isaac Clothes
Fox - Classic Fox
Falco - Classic Falco
Wolf - Classic Wolf
Captain Falcon - Helmetless Captain Falcon
Isa Jo - Isa w/ Saki Clothes
Pikachu - Accessories
Jigglypuff - Accessories
PKMN Trainer Gold - Classic Gold w/ Classic Skinned Pokemon
Genesect - Shiny Genesect
Awakened Mewtwo - Original Mewtwo
Marth - Awakening Marth
Robin - Female Robin
Chrom - Dread Fighter Chrom
Ness - Ness w/ Ninten Clothes
Lucas - Lucais w/ Claus Clothes
Mr. Game & Watch - Diving Suit Mr. Game & Watch
Ice Climbers - Hoods Down Ice Climbers
ROB - Japanese ROB
Takamaru - Captain Rainbow Clothed Takamaru
Sheriff - Classic Styled Sheriff (if they pull a Pit and update him for his normal costume)
Shulk - High Entia Shulk
Wii Fit Trainer - Male Wii Fit Trainer
Sonic - Classic Sonic
Pac-Man - Classic Pac-Man (not original, but more older styled 3D)
Mega-Man - Helmetless Mega-Man