How big are the busses, and how much leg room do you get
Better specify which buses you are referring to. The Rick Steves tour buses?
If asking about public transit buses, the typical city bus is open seating with plenty of leg room but if asking about an intercity bus then it is standard row seating with limited leg room. It will be better than an airplane but not terrific.
If you are asking about Rick Steves' Tour buses, you might get the best perspective from the Tour Experience Video. Typically, we use a 50-passenger bus like the Heidebloom bus shown, and just 24-28 tour members can spread out between them. Due to the range of destinations served, we employ more than one bus company some bus configurations can be slightly different.