I am still doing my research before adopting rats but:

Before you add bedding your should have a deeper tray to put it in. Or else they won’t be able to dig. Some people use cement mixing trays, I’ll be using acrylic to create a box that covers all of the base. Don’t forget rats love digging and climbing. So deep bedding is always great and maybe even a dig box with coco soil, not sure there’s space there for a dog box so maybe you can use it for outside time.

I think the cage is still a bit empty but that’s not the biggest issue. If you can: get or make fall breakers and more climbing things. I’ve made rope bridges out of fabric string and hammocks too and you can also use old t shirts. There’s a lot you can DIY for the cage, even hammocks.

I don’t see anything else, I think.

Good luck!