Sounds like a great trip, but here is some advice on the European version. Some of this is pretty basic stuff, but since you asked for any advice, here is some:
-Western Europe is more expensive, but some countries such as Spain, Portugal, and Italy are still relatively cheap. Scandanavia and Switzerland are very expensive.
-Some countries lack hostels. Italy seems to have a lot less than it should. Outside of Prague and Budapest, hostels can be tough to find in Eastern Europe, even in major cities of countries like Poland, Slovenia, Croatia
-A Eurail pass is usually your best bet to move around Western Europe. You can hop on and off any train for a certain time period. Also check cheap airline companies like Easyjet and Ryanair. If you book far ahead enough, you can fly for unbelievable prices. Don't buy an Eastern Europe rail pass as train fare is very cheap there.
-Be sure to check out some of the smaller towns during your visits. A lot of times these will be better than the more popular towns and always are cheaper.
-Don't feel the need to go to every major city. Look in some tour books. See what cities match up your interests. Some towns I went to just because they were famous, but then realized that they did not really offer anything that interested me.