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.