I did not see one using wheelchair. You may have to enquire at the counter. The walk is not very difficult and hence does not have any place to sit on the way. You csn view the amazing fall from the upper deck and avoid going to the lower deck, which requires you to climb down some steps.

I'm of the opinion that the more venues for which you can pre-purchase tickets, the better. Most places during the high season are crowded and I suspect that people start lining up somewhat before the open. Pre-purchasing means you can skip about 50% of the wait time. The only real downsides to pre-purchasing is that you can't do things on the spur of the moment and if it's a weather dependent thing (like the helo ride), then the weather may not co-operate...

We didn't see any. We just left our luggage at the motel. They held it even after we checked out.

Yes there is a large car park

Yes, that is when I went. Cool weather...perfect.

Preparing to be there right at opening should be little to no wait. Enjoy it!

First do the boat. The falls have a lengthy line and usually a time assigned. Both attractions are about 1km apart from each other. I recommended walk and enjoy the view.

You may want to do some research online. The website is pretty helpful and can further direct you.