We traveled first class and it's the most comfortable way to travel. But if are on the budget standard costs more than sufficient. Quite often first class will offer more really sees wifi access and some form snacks. Passes can be pre ordered from the country of origin. A variety of pass options available which allows trappers flexibility passes for travel plans. Scour the train pass websites before booking as quite often they have discounts for certain times of here for the students and seniors.
The passes allow you to use a multitude of train companies whether they be a train service or a train service that goes through several countries. This is an advantage as you are not struggling to find a certain type of train you can use the passes of and wasting precious travel time.