1) Yes - we were mostly very close as a subject group, we had a facebook group for our course and were in touch most days. During uni weeks we obviously spent all day together, went for coffee together in our breaks and often went to the pub at the end of the day. I live about 30 miles away from the university and my placements were near where I live, so I didn't see people during placements other than if we went out for someone's birthday. But I know people who lived near each other/near the university still did meet up at weekends.
2) During uni weeks you have free time pretty much all the time - you might get the odd piece of work/reading to do but you'll have free time every evening once you've done it, and all weekend. Make the most of it!
On placement it's still possible to have a bit of time for social activities, just not loads. Personally I always worked most of the evening Monday-Thursday (sometimes just a few hours then I could take a break, sometimes til pretty late). I always took Friday night off work and just relaxed, made dinner or got a takeaway, spent time with my boyfriend and had a few glasses of wine, or occasionally went out with friends. On Saturdays I spent the morning working (planning lessons for Monday) but went to my dance classes all afternoon on then took the evening off (to socialise with friends or relax at home), then worked all day Sunday.
3) I wouldn't bother joining societies personally, but some of my coursemates (who had moved to the city from further away so didn't know anyone) did. They went to a few socials or activities in October/November then stopped once placements kicked in and I don't think they bothered going back.
Regarding whether to move or stay in your current flat, I had a 45 minute commute (minimum - usually an hour in rush hour) to uni and it wasn't a problem. The university took geography into consideration when organising placements (I know this isn't guaranteed but basically it made more sense for me to have the placements I had, as it would have been a long commute for anyone else and impossible for someone without a car) so my schools were 30 minutes and 15 minutes away.
Personally, I'd stay where you are. It's not
that far - you might be lucky with placements and if you're not, remember you could have been equally unlucky even if you'd moved. Having friends around and good support is really important if you're having a hard time, much better than sharing a house with strangers. And you can still make friends with people on your course, just maybe not see them as often as you would if you'd moved.
Good luck!