First, you're going to have an awesome time. I did the same thing over the summer and it was amazing.
As for where to stay:
http://hostelbookers.com
This site is good for reliable ratings on hostels all over Europe.
http://www.europefamoushostels.com/
This chain of hostels has one in pretty much every major city and they are usually the best around. BOOK EARLY, or you won't be able to get good ones.
Yes, EURail is great. Reliable and easy.
Since you're looking to get [censored] up, keep an eye out for pub crawls. They are for tourists and lead by people that know the area, so they will take you to some random cool as hell bars/pubs that you would never see otherwise.
I went to the first 4 places on your list, so if you have any specific questions...
Also, my fav place in Europe was Spain/Barcelona, especially awesome since you want to party. I know it's in kind of a weird spot since you're flying into Paris, but if you can swing it...
Have fun!
-Craig