[souffle]

Everyone will have different thoughts on this one but if it were me I would leave it in and I would use that as the place I want him to nest. I'd rip up loo roll and take the stuff from the tube and put it under the shelf. He may sulk for a few days without his tubes but he will be OK. I don't think there is room for a box in there so I'd personally leave that for now. Give him some loo roll tubes to trash. Watch out on the size of the wheel and that it is still big enough as he grows. It looks OK for a young syrian at the moment. I'd order the cage and get it set up when you are able to have the money for it.
Keep the other cage as a clean out cage I'd say and work hard on the taming so he feels secure and ready for the move when he has a new set up.