He'll be fine for a couple of weeks
Poos aren't that dirty really - like little seeds and not smelly - and can be left for a while as well. Sometimes they eat them which is normal. They have two stomachs and can redigest nutrients from their poops. If they start taking over then you could spot clean some
I should leave his nest for now, but adding a litter tray with sand may encourage him to use it. In a couple of weeks, if you need to remove his nest then try and leave a tiny bit of the old nest behind that isn't wet, even if slightly whiffy. And put a new pile of toilet paper strips out in the cage and he'll rebuild it.