SOunds like we are doing the exact same trip. I am going London, Benelux, Paris, Spain, Switerland, Germany starting July 15th.
I was in Italy Paris and greece last summer so i did a lot of research and could answer most of ur questions.
Perfect idea on getting the things ur definatly going to need before u go (rail, air). My advice is not to book too much in advance. I ended up trying to cram too much in too little of time and ended up cancelling things where I lost deposits.
The more you travel from city to city, the more u will spend (food, metro, sleeper train reservations, little things added up)
Don't pack too much since your hiking
Bring paperback books to read on trains that u can throw out when finished
Hostelworld and this site can answer everything u need
Call your bank and let them know you are going out of the country so they dont put holds on cash withdrawls (heard that happened to a friend)
Bring neutral clothing that u can wear day and night
Factor in alcohol in budget (that put me under), that is if your drinking
IF you buy gifts for people, get them at the end. I lost mine in the mail in Paris (bastards) I did some great barganing with a street vender.
thats all I got for now. Ill think of more later. We should keep talking and if you want to meet up somewhere out there, let me know. Maybe in Interlaken Switzerland. Heard it is amazing.