It'll be on Steam on the 20th - there's already a page for it counting down that's currently at 1 day 19 hours. As for solo, the game gives you the tools to jump into a squad of randoms if you like, and generally I've found that the clear signposting towards common goals keeps it at least a bit enjoyable.
That said, in a squad of friends is lots more fun
Kirby is the man! Even if he wasn't, he'd just ingest and become one.