there are quite a few very differing opinions on rotastak cages Timmo, so asking for them may be opening a can of worms
but it is obvious that you have taken efforts to create an interesting and spacious home for Alfie and Oscar.
Given enough pods some of the issues of space that just using starter units raises can be minimised, and I see you have extended quite a bit to create lots of room for your dwarfies.
I have never kept dwarf hamsters in rotastak I must admit (in fact Ive only kept 3 dwarfs ever!) but I think I read somewhere advice that dwarf hamster pairs/colonies not be kept in cages with tubes as they can each decide to set up their own 'territories' and can sometimes fight in the tubes. I might be confused about that though?
Have you found any problems with this?