Luna has a 29cm wheel in her detolf. It's in an area straight on the glass bottom. still a gap between it and the lid, and she can run fine
It doesn't take up that much room in the cage to be honest!
No idea with how many liters of bedding. I have one end of the cage full almost up to the lid, and the other end only an inch or two (and then the wheel). I get the 10kg bag of fitch for £17, and it's lasted a long time- you don't need to replace the whole substrate when you clean out- I spot clean every few days and take out a 1/4 or a 1/3 every few weeks, replace it with fresh stuff and kinda 'mix' it.