J62

One thing you ought to be aware of is that not all trains between cities are created equal. Regional trains stop at every town while express and inter-city trains make far fewer stops. Make sure you are on one that has as few stops as possible, and definitely as few changes. I do recommend that you become familiar with train station names (very big cities have more than one station), typical travel times, and changes. The Vienna - Budapest - Prague legs all can be no-changes on an express train. You may have to change from Salzburg to Hallstatt to Vienna.

Myself, I like to print out a list of all the departure times from point a to point b so I know my options. Others are correct, you are usually better not being tied to a specific train/departure time, at least not too far ahead. (you can decide a day or two in advance and stop by the train station to reserve a seat if you wish. This might not be a bad idea on some of the longer legs. It will be good to know, for instance, that it's 7hrs from Budapest to Prague. You can leave at 6:10 am or 10:10am and get in before dark.

wwww.bahn.de is the best website, and they'll have Austrian, Hungarian, and Czech rail info as well.

You will have no problem finding the right train/platform. Each of the stations will have large boards in the main area showing which train is on which track, and the will all be in order 1,2,3,..9, 9 3/4, 10, etc.

Gute Reise