I don't think you should concentrate on getting used to your courses and reading a few textbooks on them - enjoy your summer of course, your going to have a lot of it, so try to use this time. Maybe you can only do a bit of reading, but I think this is only just to see how the courses will be like, not really reading to be ahead of people.
I think that the place you want to go should be up to you - remember your going to spend two years there at least, and if you don't like it, then you maybe will drop out and have more problems.
I wouldn't really go to extra classes to prepare for AS - see how it goes, and if you want to have extra lessons - support lessons, then you can.
But I would enjoy the summer and forget about school/college until near the results day.