You can make 2 to 300 euros a tour in tips. My best friend did it in Berlin. I'm not going to be there long enough though I'd say it has to be at least four months.
When I was a kid my mom would take my brother and I on shoestring budgets through Europe so I did the Berlin > Prague > Vienna > Salzburg > Munich trip in 2001. Amazing train rides. I do want to check out Dresden now that it's been built up and I would love to take some chick out to Potsdam for a day trip.