Are there places to sit through out the museum? I have to sit semi frequently, so standing for long periods of time is hard for me.

Yes. Throughout most of the mueseum there are benches that you can sit and enjoy the art from.

Yes, there are plenty of benches, I think you'd be comfortable

My favorite place to sit, although quite isolated by itself, is the window on the mezzanine overlooking the food court. There were two beautiful leather chairs overlooking the trees... Plenty of resting spots throughout!

Actually, visit one of the information desks on concourse. If you ask for a portable stool, like a cain, they will be happy to provide one for you. Also, feel free to utilize any DMA bench.

Yes. There are plenty. You need not worry!