Generally speaking, most rides in
Disneyland will give you a return time when you are using an ECV. The procedure is really all over the place so it’s best to just talk to a CM at each ride and they will tell you what to do. For example, we were told to just go into the exit of Pirates and they would get us on a boat without a return time. I was never able to find comprehensive info online about the procedure for every ride so I basically had to wing it. All the CMs I’ve encountered have always been very helpful with this.
Certain rides in DL that have been refurbed or built more recently will allow the ECV in line.
I *think* all rides in DCA allow you to take the ECV in the line, but there are many rides I haven’t tried that on so I don’t know for sure.
Parking is pretty easy. You’ll see places where there are a lot of ECVs parked so you know you can park in those areas. I’ve also been able to park it in very random, out of the way places where mine is the only one and it’s never been a problem. I think I’ve had mine moved by CMs if they were trying to rearrange an area but it’s never been moved so far I couldn’t find it.