In reply to camhead:
There's some information here that should answer a few of those questions:
https://www.ukclimbing.com/forums/t.php?n=663360
As regards finding partners, there's a couple of Facebook groups that work quite well:
https://www.facebook.com/groups/bohusstugan/ and
https://www.facebook.com/groups/391522367557471/ Everyone else posts in Swedish, but plenty of non-Swedes seem to manage to find partners on there - if you stick up the classic 'Hi, my name's X and I'm planning on visiting between Y and Z dates', you should find people, and if not you'll likely meet people around! Plus, a lot of crags have bolted lower offs or trees, so you might be able to get by with your girlfriend belaying you but not necessarily seconding if she'd be alright with that.
A few other thoughts:
Definitely rent a car, as the public transport there is a bit crap and the crags are quite far from the BKK club hut (which I heartily recommend, particularly as there are mattresses inside). Your girlfriend might well struggle in terms of grades - I believe 6-, which is where Bohuslän really gets going, is roughly equivalent to 5.10 (but might well feel a little soft if you're already proficient at granite jamming), but there are a few crags that offer decent easier routes (
Nordens Ark is the main one, and
Jungfrun (n4) is a wonderful two-pitch route that is very close to the hut, but there are others). If you're climbing 5.12 (roughly Swedish 7/8) you'll have a lot to go at, much of it very spectacular -
Hallinden and
Häller alone should be enough for a short trip!
If you need any offer info, feel free to email me.