Are the rooms large enough for walkers? Also are there benches to sit on?

Yes definitely, they are large enough for a walker. Also There are many benches and places to sit throughout the whole place.

There are plenty of places to sit briefly, although they are not very comfortable. I have difficulty standing for periods of time and found the benches and "rocks" to be just fine to take a break for a few minutes.

Yes. A walker can move throughout the facility. Lots of places to sit throughout, as well.