[Pebbles82]

I think if it means he has to go in his old cage, it would be better if it was for more than a week to let him try and settle - as it would stress him to change cages again so quickly, even if it was to a better cage. You might need to play it by ear. If he is bar chewing and going bonkers in the little cage, you'll need to let him have quite a bit of out of cage time (eg in the dry bathtub with a couple of toys unless he is fully handtame - even if he is tame it would need to be in an area where he can't escape or hurt himself). He would probably manage with the flying saucer for a week or so. Just give him lots of nesting material and some kind of cardboard box house (tissue box eg) so he can retreat somewhere and feel safe.

If he doesn't seem stressed in the little cage then maybe best to just leave him in it for 2 or 3 weeks at least - then when you move him to the new cage, get it all set up and take the bar top off the old cage and just put the whole cage base inside the new cage on top of the substrate, without cleaning or changing anything, so he can gradually explore out of the old cage into the new one. After a week or so if he's using the new cage fully you could take the old base out but take the substrate out of the old cage and any toys and put them in the new cage where the base was so it still smells familiar. If that makes sense!

The reason changes and cleaning cause them stress is because hamsters scent mark. They don't see well at all and when they move into a cage they spend the first couple of weeks scent marking everything so they can find their way around - they have scent glands in various places. So if a cage is completely cleaned out weekly they are lost - it's as if their home has been ransacked and smells different and they can't find anything! So when changing cages it's important to not clean everything first - it'll be fine for a couple of weeks then you can spot clean or wipe the odd thing when necessary. They are actually very clean little things and wash themselves a lot.

Re the hamster potty/litter tray - you can use any dish for that really - a household dish or shallow casserole dish eg if you don't want to buy one - but it does need something like Chinchilla bathing sand in - that soaks up the pee. Sand needs to be special sterilized sand - eg the Chinchilla Bathing sand i linked (must be sand not "dust") or some people use childrens play sand which I think you can get from Argos. Just check it's sterilized.