This is the largest one I've ever seen. It was at the expo last year. He actually climbed up my arm and sat quietly there for a bit. It was probably the length of my hand.
I have 2 marbles, and they are in a 60x40x40 URS enclosure. This pick was taken a while ago. I've now got a gecko cave attached, and other hiding places. I just need to work on a slate stack type thing for them to hide in. I think I have a boy and a girl, so I wouldn't be adding more to this enclosure. They do like their own space, although I do catch them on the odd occasion sleeping together in the gecko cave.