zippered

I'm trying to plan a trip for about 3 weeks this summer. My boyfriend is going to have to work 3 days a week, with offices in Amsterdam, Paris, and London. He obviously needs to space out when he's working, so I think we may need to zigzag a bit.

My initial idea is as follows:
London - 4 days
Brussels - 3 days
Paris - 4 days
Luxembourg (maybe) - 2 days
Brugge - 3 days
Amsterdam - 4 days
Cologne - 2 days

What do you guys think of this as a plan? I've never been to Europe before and am being given only a month (during finals) to plan it all. Also, if anyone could give a general estimate of cost per day (with staying in hostels and all that), that would be appreciated.