Need some advice from the pros about interrailing around Europe!

I am going interrailing with two of my friends (all of us are 21 years old and male- if that helps?) from the end of July to mid August. We are getting the 22 day global pass and are actually starting in Barcelona as we have got cheap flights to get there. Although it is only 22 days pass that doesn't include 3 nights in barcelona (as we are not using the pass til we leave there as we wont be using it in Barca); so we will be going for 25 days. The route is:

Barcelona

French Riviera

Milan

Munich

Prague

Berlin

Amsterdam

Brussels

London (Home).

The plan is to stay 2 or 3 nights in each city. None of us have done the whole travelling thing before and so don't quite know what is right and wrong in terms of money and what to take (how much clothing, do we take a lot of cash or rely on card machines, etc). One of the main issues that I have is the amount of money I am going to need. I think I can get around £1700 (after plane and interrail tickets) in money to take on the trip. So obviously that has to cover everything, from accommodation to food to going out. So that should give me about £68 a day.. Is that going to be enough in the places we are going? What are the places on the list that will cost me most? Obviously we will be drinking, etc in the nights and sightseeing during the day, so I am worried this won't be enough money. I am assuming that barcelona, french riviera and milan will be the big hitters in terms of alcohol costs and accommodation prices? Basically just asking you guys (and girls) for some guidance about money and what to expect to be spending for what in the places we are visting. Also any help on what I should pack (such as essential items that I wouldn't want to not have in my luggage) and how many sets of clothing, would also be very helpful.