Wow lucky ham! So much to do.
Good to hear that you will be upgrading him to a larger wheel.
•Have you got a sand bath? Maybe put some sand in the litter boxes if you haven't already.
•You could remove the ladder that goes to the shelf and just put as much bedding as possible under the shelf for him to burrow in. Alternatively you could get a cardboard box and cut the top and bottom out and use it as a burrow box.
•I'd add another water source personally as bottles can jam.
•Ditch the food bowl and scatter the food. Foraging is really enriching for them and it'll encourage him to move around.
Honestly though there isn't much I'd improve on as you have a lovely set up.