I want to learn, but not sure where to start

[Garamonde]

Well you'd need the original SSBB files. I'm not 100% sure but they are probably BRRES's. BRRES Viewer can only open BRRES's (and sometimes CMD, BIN and ARC). If you want to open RTB's files you'd need a modeling program. That's something RTB or Apoc could help you with. I'm not sure if Brawl would be the easiest thing to start with, but you can try it first if want.

I didn't know there were still models to be ripped from that game... by any chance could you send me those Brawl files too?