I wouldn't say Luigi should count as an echo, he's different enough from Mario for it to count.
Ganondorf is questionable, since he's basically "Captain Falcon, but slow", yet from a completely different franchise. I think he's slow enough that it doesn't count. Plus, if I could, I would have him focus more on sword moves. I know they've started changing some of his moveset to use his sword, but there needs to be more.
I'm not sure if it's possible in their menu to have more than 1 echo fighter per character, so maybe Toon Link can be standalone. Young Link is basically the same as Link, but Toon Link has some quirks that make him stand out a little more.
Falco should be an echo, but Wolf is different enough to count separately.
the fox trio needs different goddamn final smashes, though