My current guesses for the roster:
1) Goku
1.1) Goku Blue
2) Vegeta
2.2) Vegeta Blue
3) Gohan
4) Ultimate Gohan
5) Future Trunks (Ikari install)
6) Vegito (Blue install)
7) Krillin
8) Piccolo
9) Gotenks (SSJ3 install)
10) Freeza (Golden install)
11) Cell
12) Majin Buu
13) Kid Buu
14) Android 18
15) Beerus
16) Hit
17) Merged Zamasu (Final Boss)
18) Broly
19) Bardock
I feel like every character on this list is 100% guaranteed to be in. They amount to 19 characters + 2 clones.. which seems reasonable by Arc standards.
If they decided to up the roster to 24 characters, I think those with highest chances to be in are:
20) Android 16
21) Android 17
22) Master Roshi
23) Tien
24) Yamcha (Joke character)
Other possibilities can be Captain Ginyu, Raditz, or Nappa. I hope none of them are in though.
for the DLCs, I think we're getting Black, Caulifla, Kale, and Jiren. That would be perfect for Super representation.