[Kissa]

If I were you, I'd fill the base of the alexander with substrate -- it provides plenty of cushioning in case of a fall, and gives lots of digging opportunities. Although it does mean you'd have to put the wheel on a shelf, I believe the alexander is tall enough for this though. Both of my hamsters have their houses buried in their substrate -- they started doing it themselves and I thought it would be good insulation for winter. They only have one each, though. Oh, and I'd advise you to plastikote or something the house/burrow maze thing. I had one for my Syrian and she took to peeing inside it, and because it has a floor in some of the compartments, the pee couldn't drain into the substrate.

I believe PVA is a good plastikote equivalent. It's child safe, so I'd be comfortable using it with hammies.