We've only done one visit with an ECV so not a ton of experience.
It really depended on the ride. At most rides, we'd have to ask the TM where to park, most weren't 'far' from the ride entrance, but weren't 'close', either.
My wife was able to walk with a cane, so we didn't ever ask for a wheelchair. Not sure if you can get the wheelchair before you get in the queue or if you can have someone in your party get it and take it to the parking area.
Sime areas even changed - for Hagrids, two out of three times, we parked near the queue entrance, but walked up the exit path (it's kind of a long walk and all uphill). The other time, the TM told us to drive the ECV up the hill and park it just outside the exit making it a very short walk.
The only queue you can take the ECV in is the Hogwarts Express line because it drops you off in the other park.
