I sure hope they don't tie DLC characters to amiibo and overcharge for them. Amiibo is a great idea for kids, but I certainly don't want to have to end up buying toy figures to get extra characters in my games...
People say that Valvga will be playable, and he's not on the character select screen, so it could be as you said earlier - a separate page for villains with more of them to come, leaving still 3 slots for heroes. I sure hope so anyway.
I really can't understand why this game is so centred on OOT, TP and SS - it really really needs to spread the love for many of us who grew up on the older games and love the handheld games too.
I don't want to complain too much either - I am thankful we're getting something like this, but it's leaving still a lot to be desired.
I guess there is the possibility that it will get a sequel or... even some Ultimate Complete Edition in the future with more characters... This IS a Warriors game after all.