For starters, you need to download brawlbox to basicly everything here. When you got that you can edtit things like SFX textures models and other things.
It is im portant to know if you want a custon charcter selection screen then you need to have riivolution, (can be downloaded
http://rvlution.net/riivolution.zip) and template.
http://rvlution.net/riivolution/images/a/ac/SSBBtemplate.xml Right click this and save as...
once that is sorted hacks you've made go in ssbb folder the root of your SD, and also the template goes in a folder called riivolution (folder also9 needs to be at root). and the riivloution app goes in a folder called apps (BTW you need to create these folders your self) at the root of your SD. then run riivolution through homebrew and and click install! and then your sorted!