I have ms too and used a scooter on my last trip in September. I couldn't have survived without it. . I drove forward to get in and out of the buses. I had a scooter from all star scooters and I think it was a regular size one. Smaller than the ones at sam's club. Most of the time I parked on the left side. You just pull forward and park like a car. If there are multiple scooters on the bus, in my experience they fill the left side first then the right. It only happened once for me. 3 scooters on bus and I was on the right. I had no problems the drivers were nice and helpful even if it was a bus they weren't used to. They will park it for you if you get stuck.
Getting out is easy too my scooter had a really easy turn radius. I would back up a little turn the wheel and slowly behead for the door. Make sure you are on the ramp for the back wheels.
I also tried to remember to put the speed toward turtle so controlling was easier. Don't let the line of people worry you that you need to hurry so they can get on just ale you time and have a great trip