A Couple Questions About My Hedgies Home.

Currently my hedgehog lives in a "Critter Cage" with these dimensions:

L: 24.00  W: 12.00  H: 16.00

Half of the cage has a heating pad under it, which makes the cage a bit warm to the touch, however not hot. There is about 3-4 inches thick of bedding(which he could honestly spend all night digging through) and a bottle hanging from the top of the glass, and small wooden home that he sleeps in(however sometimes he just buries himself in the shavings). He is currently 18 months old.
I have a few questions. The first is has anyone heard of a wheel that works well in a glass cage? His wheel is currently a free-standing wheel that he often tips over.
The second should be prefaced by first refrencing the breeder my hedgehog was purchased from. She stated that hedgehogs are very hard to litter train, and it's often impossible. I have however seen quite a few hedgehogs that are litter trained (with fleece bedding, as well) and am wondering if 18 months is too late to litter train a hedgehog.
The third is: Do you think this home is too small? Many of your hedgies live in mansions that I could only dream of being able to provide.(Perhaps when i get a new, 2 bedroom apartment which I am looking for)

I'd like to thank you for any help you can provide, and although is a very demanding first post I have spent quite some time 'lurking' this website, and really do appreciate most of the information you may have.

Is your cage too small? In my opinion yes. There are places that state 2 square feet, but that is way too small for a hedgehog. Aim for something that is at a minimum 4 square feet.

You'll find many people do not care for glass cages. They are often heavy and difficult to clean properly. Plus they often do not allow for good air flow. Take a look in the housing section. There is a thread in there for examples of cages. You'll find a lot, including those that are expensive (Ferret Nations) and those that are cheap (clear storage tubs combined with tubes). Small apartments can be a hassle to provide the floor space required, but take a look in that thread, you may find some examples that will work for you.

Can hedgehogs be difficult to litter train? Yes. Some never will. Even those that do litter train will still go to the bathroom on their wheels.