I just graduated this year, so I'll help you out.

You live there.
The classes are less often.
Tests are given more weight.
Frankly, there are tons of differences, I can't really name them all.
If you are good at getting a long with people in high school, that will carry over. However, if you aren't good socially it will still be easier to make friends because of the larger amount of people; the more people there are, the more likely you will find a group of people who share similar interest to you.

Also, join as many clubs and activities as possible. You don't have to stay with all of them, but it does help you make friends faster. For example, I learned to play trumpet and did band my freshmen year. I wasn't very good, and I quit after my first semester, but many of the friends I made in that short time in band I still hung out with all four years of college.
It really depends on the class, but I'd say 2-3 hours is about average. However, I did have some classes where I didn't really need to study more than half an hour or so, and some where it was as much as four hours.
Only if you let it be. I still played video games, went skiing, played guitar, and pretty much all the other things I did in high school. I had to restructure my time a little, but I still managed to have fun.

By the way, what college are you going to? I went to University of Maryland Baltimore County.

I actually avoided that by going vegetarian my first year; though I doubt many others would be willing to do that.

One thing about my college experience is that I never had my parents take me there my freshmen year. After I graduated high school, my parents moved from Maryland back to Puerto Rico (we had been living there up until I was 8, when we moved to the US). I stayed with them over the summer, then I flew to Baltimore and took a taxi from BWI, showing up at the college alone.