Some hostels will not allow men and women stay in the same room, and some will....you will have to email ahead to be sure...you do not want to be left int he cold, as a couple you might wanna spend the extra money and get yourselves a private room...still a hell of alot cheaper than a hotel!
Cities to recommend??? this will depend on money, and how you are traveling..rail pass? rent a car? bus??
But here are my top 7 cities in Europe
Monaco City, Monaco
While you are trek'n, don't forget the small towns, you will find hospitality there more welcoming than the larger cities.
For you must brings, go through this section of the boards and see what others carry in their packs...
A couple of things I would not forget utility knife ( swiss army type), my own fork/spoon, photo copies of all documents including travelers cheques.
Weather??? try this link here...Weather Network
Should give you the averages for the April...
And on a final note
To the TravelPunk family!!!! Always nice to help out a fellow trav'la