I never really missed home too much. It thought it was so exciting to settle in, and get to know everything that's new around me. There's tons of info floating around that you can read about different stages of culture shock,...but I had a much bigger problem with "reverse culture shock". But as long as you are prepared, and know what you can expect, you will be fine. It is great that you've decided to do this, and I'm happy that you were accepted to all these schools.
As for deciding which school to choose--that's something only you can do. You probably know which program you're most interested in...but I had a friend who went to Queen Mary and loved it. I've visited UCL and King's, but it pretty much depends on what the individual departments are like, and which you think would be the best fit.
Someone else said that there's generally a 3 week break in March/April, so what you decide to do during that time is up to you. I used it to travel all around Europe, and loved every minute of it

Also, if you're looking for a place to live, I remember getting a whole booklet on student housing from an open day at either UCL or Imperial...but if you wanted to live in a houseshare or something like that, you could also check out spareroom.co.uk
As for all the financial questions--I have no idea! But i do know that US student loans are accepted at UK Uni's, so you might be able to contact the individual schools to see what you need to do.
Congrats and Good luck!!