It's perpetually in progress but what's there is already pretty much a complete game, dev just can't stop adding/revamping things. I've played it like 5 years ago, spent 50+ hours and had a great time. There's also an active modding community.

There is a lot of game there. It is like Mount & blade in space so don't except a story or something like that. You make your own. Totally worth the money.

There is quite a lot of game and there is a solid modding scene as well. It is worth the money.

More like Project Zomboid or Warframe. They could be released as version 1.0, but they just always have ideas for more things to add, and they do it in a way that doesn't make the experience feel incomplete, just that it feels better when there's new stuff added.