I work as a shop manager for a company that deals with a lot of tour/charter bus operators in the NYC area.
To drive a full size coach with passengers you need a CDL class B with Passenger endorsement and airbrakes. You also need a current physical.
As for DOT stops, passenger coaches tend to get stopped and examined while parked VERY often in areas like Atlantic City, other casinos, amusement parks etc. It is EXTREMELY common for a bus to be put out of service while still parked awaiting its passengers who are having fun on the roller coasters.
We try to impress upon our customers that a pre-DOT inspection by us, will save them money in the long run because being put out of service a few hundred miles from your home base and then having to get the bus towed a few hundred miles, is not cheap.
As for the stress level, its probably on par with truck drivers, with a little less loneliness.
The business overall is getting VERY difficult for the smaller operators due to rapidly rising fuel costs as well as rising insurance costs for the coaches and prices on parts increasing due to the raw material costs going up. For example, we have an MCI 9 in the shop right now, and one rear engine bay door (stainless steel) costs over $2000 yes, TWO THOUSAND dollars... and the door is only about 24" x 30".
If you have any questions about the business, give me a PM and I'll try and help out
-Dan