Tricky choice. I think I would choose the wheel after the cage. ie the wand chooses the wizard
Kind of. Easier to get a wheel that goes well with a cage than trying to get a wheel you've got to work with a particular cage. Either of those would be fine. With a free standing wheel though you will have restrictions on wheel height in the substrate area and I always found that annoying. There is also the wodent wheel. Only Rodipet seem to sell it now. It doesn't screw to the bars but it hangs from the top well. Although the cost of it plus postage makes it almost as expensive as the Silent Runner.
I'm biased towards the Silent Runner so see what others say