Deborah:

I don't have accessibility standards at hand, but centering at 4'10"
sounds a little high for wheelchair drivers, especially if you have a
passel of small pieces.  Check "Everybody's Nature," by Carol Hunter, Jan
Majewski's works, or the access design guideline available through the
Canadian Paraplegic Association.

One good way to check the suitability is to test-drive it yourself.  Get
in a wheelchair and wheel through one of these exhibits yourself.  You
might be surprised at what you'll see.  When I did that on one of our
exhibits, I not only found that I was getting a crick in the neck from
looking up at a lot of small framed pieces hung high, I couldn't see half
of them anyway because all I could see at that angle was ceiling light
reflection!

Tom Vaughan
The Waggin' Tongue