Hello.
First 1.9 then 2.0 and after that steam release. All versions will feature new content, but steam release will differ from 2.0 only by having 1 exclusive character and it's questline (that's what we know as for now)
2.0 will still be free on itch for everyone to play.
Considering next side project - it can be anything, not only starmaker spin off. But if we speak about it - it's story and characters will be completely new, so you won't see known characters (apart from a maybe cameo).