Ok arcade styles are good, but very limited.
I would suggest to keep using 16 bits style characters (snes, megadrive/genesis...)
It covers most of the story characters and there is plenty of resources about them.
Every single character of the anime have been sprited, even non fighting ones...
This is the best choice IMO.
Also they are easier to edit.
Francot,
Just start to edit a regular mod.
Change only one character, your player.
Transphorm it in a regular Goku character until there is no more graphics or sound from the initial character (Maxima??)
If you're not satisfied edit again, test, edit again, test...
When it's OK try working on enemies, stages and other players...
I'm sure there is potential in a DBZ game like that.
Good luck