Think of it like this: There aren't even going to be abilities specific to each amiibo. For example, Meta Knight as well as Link will most likely have the Sword ability as their amiibo power-up. Even though I have both, they would basically be the same thing in this game. You'd only need to buy one amiibo.
Which in itself is actually really cool, that way if I really wanted to I could buy an awesome figure for other games (since it works universally for games like smash as well), and not have to grind on a specific level every time I lose my favorite ability! And if I really wanted a challenge I could just, well, not use it. If anything I'm still of the mindset that this is a really neat design and works very well with the amiibo.
After thinking about the amiibo feature, to not have to have a N3DS and use it you'd need an amiibo adapter which I have seen absolutely nowhere in any stores I have been in in my city. I probably won't even be using it in the first place.
And on the topic of amiibo has ANYONE here seen a place to easily get a Robin amiibo?