You can visit them wherever they are, whether that's your galaxy or another. The Galaxy is pretty huge, I'm still in the starting Galaxy and nearly all of the systems I've visited have not been uploaded before. Plus certain mechanics you unlock make playing together easier (sorry don't want to spoil story/discoveries). I bought my key from CDKeys back when they were £15
I was thinking grabbing this as I tend to like open world, base building games. Good to hear there's often patches, means the devs are still active even after all this time and many free updates, which is really nice! Multiplayer sounds like fun, so you basically visit their galaxy and vice versa?
I've been playing this a lot to distract myself lately, it's very open-ended but there are questlines you can follow etc. My main goal atm is to reach the center so been going black hole hopping. This is a good price, be aware patches are big (the last couple of weeks we've had multiple 4+gig patches) Also multiplayer is interesting, can visit friends wherever they are and play together.
It is a good deal money wise but if i had to buy it again I would have bought it straight from steam to support the devs and not from shady cdkey sites.