I only went London (including Scotland) and Paris. One city is for one week and it is 2 separated trips. I feel really exhausted for each trip. Maybe my travel plan was covering too many spots.
For me, London is similar to Paris. But Paris is more attractive. I like it more and there are much more interesting thing to see and many delicious food to try. All expense in London is very expensive. It is not very easy for your driving in the big city (thing about China. Europe is very similar to China. High population and limited land). Since it is hard to find a parking place and you need drive in many very small road and parking in a very narrow parking lot. Hehe...it will test your parking skills. The subway/MRI is very efficient way for traveling in a big city.
You can take the train between cities.
For saving accommodation cost, you can find some short-term renting apartment for student. It is much cheaper than hotel. Of course, don't expect you got the same level service in the renting apartment. For safety, find some travel mates with you. If you are 1 person, just find YMCA or B&B. Maybe it is a good choice.
Thief is very common in Europe. I heard so many cases. So keep your passport, tickets and money safe.
The power socket in Europe is different from North American, so find some socket transferer for your camera, camcorder etc...
The travel in Europe is very similar to travel in China. So just follow the similar way.
Good preparation will give you a relax and excited travel fun...