I would rather use "della" than "per la", but sometimes we use "per" as well.
"Risposta rapida" is fine, but "rapida risposta" is more natural. Here http://italian.about.com/library/fare/blfare129a.htm something on the topic, but "rapido" is not on the list. Sorry!
You can remember a short sentence to remember that "DI". "Grazie di tutto", "Thanks for everything", that is pretty useful, especially if you go to Italy and somebody who doesn't speak a word of English bring you to where you need to go because he cannot find a way to explain you how to do it. :D