No if it's stopped smelling it should be fine
A week was a guestimate - some things are pongier than others. 28cm is fine - for all but the most enormous Syrian, and if that happens you can upgrade later. A platform for the wheel sounds like a good idea - so you'd want the platform sitting just above the substrate for that I guess. With a tank like that and the height you have I would put at least 20cm of substrate in and pack it down well. A lot of substrate but you shouldn't need to replace it all in one go and can just spot clean and replace half of it every 3 months or so - especially if your hammy uses a litter tray (they tend to use it if you put it in the corner they choose to wee in).
I've found if my hammy has a large house, he moves his wee corner into the corner of the house. So I have the litter tray inside the house - and got a bigger one so there was more room for it! But they all have their quirks. The Germans do use houses with litter trays inside though and a lift-off roof so you can empty the tray without taking the house out. But any kind of house/hide will do as long as it's big enough to build a good sized nest.
If you have deep substrate - 20 to 30cm you'd probably need light items on top of the substrate or stick little dowel legs on heavier things like a house, in case they tunnel underneath so nothing heavy can fall on them.
You could maybe have one long platform along the back at about 25cm high - so the wheel could stand in the middle and the rest is a general platform - but then you'd need a ramp up to the wheel and at each end probably.
Maybe just look around at tank set ups for ideas
I've always liked this set up and platform idea (see photo below) although maybe not the same height as the wheel sticks out of the top on this one. So having the wheel at a lower level might be better.
Another thing I've seen people do with melamine cages is mount the wheel to the side of the cage. ie drill a hole in the melamine at the right height/right place and put a bolt through or re-use the existing spindle. Then it's attached to the cage at the height you want it without needing a platform. I kind of did that in our cage with the Silent runner attached to the cage bars, but that has a special plate and bolt to do it with.
Re: Building a cage ~
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