By set I assume you mean the combination of 2 stages, 3 characters, and some costumes?
No, I don't think we'll get a set of characters. Lucas, Roy & Ryu were it so far as pre-ballot characters go, supposedly. The only other character I can see them adding before deciding on ballots would be Wolf and I expect him to drop either with the first ballot or alongside SF0 if we get him at all.
KK Slider outfit is already released in japan, it will probably just randomly go up some time for everywhere else. Maybe in August. Maybe with another set of mii costumes. Who knows
The stages & youtube uploading had no dates mentioned. Both could be in August but if that's the case I think they could have said so. Could just be random filler or could be waited for dropping with a character.
I'm also assuming one of 3 scenarios so far as characters are concerned: 2 Ballot characters & Wolf, Wolf & 1 Ballot, 2 Ballots and no Wolf
Not having Wolf at all is incredibly eyebrow raising considering he has much wider appeal than Lucas & Roy, is popular and is involved in an upcoming big game, but they could also just forgo working on him to favor Ballots.
I don't think the Ballot will produce more than 2 characters, since they will likely be all new characters that take time to develop
First Ballot, I don't know. September or November feels right, for one of the 1 year anniversaries. I say September because I'm sure they're already in the process of deciding on one based on the current ballot; they'll choose the other in October I imagine, probably for release either late that year or early next year.