While I had large vehicle driving experience, I had never drove a bus. I was a call firefighter for 20 years and could drive anything we had in the barn. It really didn't matter but may have helped getting cast relatively quick.
When I started at Disney, back in 2006, you were trained to take the CDL Class B test with passenger and air brake endorsements. I had two weeks (the Class A CDL drivers in our class only had 1 week but still had to take the DOT CDL test) of full time, 8-5 training with a trainer. We learned how to drive, how to circle check a bus, CDL passenger transport specific laws and lots of behind the wheel time to make sure we were doing it correctly and safely. We had a dedicated training area at what is now AoA where we would train on the scenario's of the DOT CDL driving test (ever try to parallel park a 40' bus?). Once we passed the DOT CDL test, we then had hub training. That was 3-4 weeks at a hub (which is a park or DTD at the time) Once we "mastered" a hub, we worked that hub for the remainder of that 3-4 week period solo. Then we were rotated to another hub. So in total, there was almost 6 months of training to be fully "certified" to drive anywhere on property.
MK covered MK routes, the Fort, parade bus and the MK cast shuttles, Studios covered just Studio's routes. Epcot did Epcot routes, the extra for the Coronado-BB route, and the case shuttle. AK was busy, you did the AK resorts/BB, cast shuttle, parade bus, BB closing and WOS shuttle. DTD did DTD and TL but at that time we has both Marketplace and PI stops. During my 5 years there I started with the crap shifts and just before I left, I had a pretty choice DTD schedule. I was a CR so I didn't even bother to bid and still ended up with decent schedules once I paid my dues as a junior driver.
I had some great vantage points for special fireworks, and worked for and with some great people. Did special events like Grad Nights, NOJ, (although NOJ at MK in the bus info booth is a never again moment) and the Children's Miracle Network golf shuttle to SOG.
I would go back in a heartbeat (once retired) to driving despite MIMs. I really enjoyed the interaction with guests.
I applied to be a transportation CM at a job fair Disney attended at the Central Florida Fairgrounds, had a quick interview and was called by casting maybe 2 weeks later for a final interview and a "No Crap" expectation of what hours would be like, etc. I had talked to a couple of drivers before hand and knew that while I was out of work, this would be a good job.