go and see @Majickhat55's tutorial :
https://gbatemp.net/threads/mini-tutorial-replacing-textures-in-sumo.457806/
we can just edit textures not models.
1-I have Helix I'm working on Peeko.
2-No also ohana3ds rebirth for Sun Moon Ultra Sun Ultra Moon.
3-Yeah go and see the firsts posts.
4-Yes With Braindump or download a rom.
@Xdqwerty, Osu! Tatakae! Ouendan! is the Japanese version of the game, different settings/characters/songs but otherwise identical mechanics. I played that before I knew about Elite Beat Agents lol. Both fantastic games https://en.wikipedia.org/wiki/Osu!_Tatakae!_Ouendan