I agree with shellonabeach about the cage.. Although it LOOKS neat, it really isn't the best for them. They have little feet. Try to stay with smooth surfaces. Petsmart should have S.A.M cages, which aren't bad (provided you take out the bottom that has lines like your cage, and just leave the smooth bottom)

As for being social.. if they've grown up together, there's a MUCH better chance they will not fight.. but if they haven't, there's a higher chance of them fighting to the point one bleeds or worse. So if you get two, be watchful. (They make noises when they fight too).

Oh, and as for not being good climbers.. my dwarves climbed stupendously! I had a couple S.A.M cages, all hooked together with these tubes for it, and they climbed up them fine, but the cage you show could cause them a hard fall... They will climb if given opportunity, and mine loved to do so, but with the tubes, if they fell it was just a slide, not a fall.