No, you don't have to take classes when you there, but some colleges required that you take classes to stay full-time. As for credit it all depends on your college, a lol of people didn't get any, mine gave 3 business credits without taking classes, and I actually knew someone who was getting 15! But she's the only person I knew getting so many. So just check with your college advisor or whoever you need to at your college.
And as schroder6452 said, if you choose the same arrival date, and then check in at the same time, your more likely to get a room with your friend.