I don't know what your circumstance is, but, I am a full time wheelchair user and while I have never done the buses, I have done the boats. Easy peasy. No problems at all.
I did see a bus unloading a wheelchair and I didn't see anything that looked like it was a problem. They just lowered this big platform, and the wheelchair person rolled down a slight incline. The bus may have lowered its self down, but I did not see that, but thinking back, the bus pulled up, dropped the platform down and the person rolled out to the sidewalk. Maybe that is why there was only a slight incline. Then there is an elevator to take up to the next level.
I know for me, it is usually easier if I can just stay in my chair when I travel around.
Honestly, this will be my second time doing universal in the past 6 months. Had a great time.
My whole group had express pass so it could be different if you don't, but when you go to ride something approach the team member outside the ride and they will tell you what you need to do and if there will be any need of a transfer. I also have to have the supervisors ok to ride. Never takes more than a few min for them to get there, they ok me, then we are taken straight to the front of the line.
Or you can pay for parking. Whatever seems easier for you.