1) it depends on the group, Durham clubs shut at 2 so people do tend to go out earlier than in big cities, for us a normal night would be pre drinking/college bar till about 10.30, then down to a bar in town (jimmyA's/fabios) then onto a club, however when im on sport socials involving a bar crawl these can start as early as 7.30/8.
How many times again depends on the person/group, im a 3rd year and this week im going out 4 times, although thats not typical. Freshers are probably 3/4 nights a week once you've been here a while (obvs more at the start), 2/3 for 2nd years and 1/2 for finalists. But as I said, this completely depends in the individual.
2) Sorry I dont
3) Erm maybe, although im a bit confused as you say every night but then say only 5 times a month. During freshers week it would definately be a problem as you would miss the organised activities where you generally get to know people. Once your more into term though you could probably manage.