17 new characters is consistent with what I was told in October last year. Specifically, I was told "over 15 new characters". Some of which are supposed to appear in the D+ series.
And to elaborate, no this doesn't mean there are only 17 animatronics (nor 22). I'm not even sure if 17 is the true extent of new ones when counting all of the animal characters. It's probably including the "focal point" critters who are playing instruments, but my guess is that there are also going to be additional "incidental" animals that will appear (like regular frogs, birds and turtles who have been seen in the art without instruments). The returning PATF characters will add a decent chunk to the roster as well. Tiana, Naveen, Eudora, Charlotte, Big Daddy La Bouff (I think), Mama Odie, Louis, Ralphie and the King and Queen I believe have all been said to be appearing.
And keep in mind that quite a few of the characters will get multiple figures. Brer Bear had 5 figures in WDW's Splash, Brer Fox had 6, and Brer Rabbit had 7. JUST Tiana, Naveen and Louis will probably have at minimum 4+ figures each. Tiana and Louis have already been seen twice in two different pieces of art showing two different scenes, and it's safe to say they'll be in the finale scene as well and likely others. Some of the other characters will no doubt have multiple figures too. I've also seen that new Otter character in two different pieces of art located in different show scenes.
The information shared with me last year thus far has turned out to be true. The one claim i'm still waiting to see pan out is whether they're going to reuse/reskin any of the older America Sings figures.