Okay, so I have a source working on Smash Ultimate. He knows who some of the newcomers are gonna be, and wishes to remain anonymous. He didn't elaborate a great ton on what a lot of these characters can do, so take some of these things with a grain of salt.
First up, there are, in total, six new fighters in Smash Ultimate not counting the Echo Fighters. These characters are Simon Belmont, Ridley, Inklings, King K. Rool, Waddle Dee, and Geno.
Waddle Dee is specifically Bandana Dee. He got in thanks to having a highly unique and creative moveset, yet very easy to work with. A lot of inspiration came from a couple of Kirby's moves without being derived from him (for example, Kirby's jab is given to Waddle Dee, except he uses a spear when doing so). Waddle Dee's attacks do have sweet spots.
King K. Rool was a difficult character to come up with a unique and effective moveset for, and even taking into account all of his appearances in the DKC franchise, still required some creative liberties in order to make him effective. My source expects him to be one of the last characters to be revealed, if not the last one due to some necessary tweaking to make him work.
He doesn't know much about Simon Belmont or Geno outside of the fact that both fighters are going to be quite technical. He does know, however, that Belmont's costumes are going to be inspired by the wardrobes of the other main characters in the Castlevania series.
He has no knowledge as to how many echo fighters that there will be, nor who is going to get in. All he does know is that there's going to be more echo fighters to show off, and that they will likely be added in based on the Smash Ballot results.
A couple characters were planned but ultimately cut either for licensing issues or due to time constraints. The only notable omission that my source is aware of is Heihachi.
No DLC is planned. However, if we do get any, expect to see Heihachi, and presumably a few other of these cut characters.
Sing it with me: