This web site is really valuable. Its not in English, sorry, but basicly its like Mapquest for public transportation systems in Holland. Its pretty good; it includes city trams and the railway system, so you could figureout what you needed to do to get from, say Den Haag to Amsterdam or whatever. Just punch in the address of your Hostel and Centraal and you should be able to find out the tram you want to take.
http://www.9292ov.nl/
Oh, and there are a gazillion coffee shops ofcourse. All the tourists go to ones like Bulldog and Grasshopper, but I like the smaller ones myself. You'll see ;)
Blake
American living in Rotterdam.