Yes, the DLCs will be released at the same time as their relevant Steps, so Step 1 and 2 DLCs will come out with the Early Access release, and Step 3 and 4 when those release.
No exact dates for Steps 3 and 4 yet, but you can get a rough timeline on our Roadmap.
Unfortunately there won't be any other character DLCs for Now & Forever, as the main game with the two leads is going to be so huge.
Thanks for following, and have a lovely day!