Thanks both the ideas are really helpful as i get a bit stuck on creativity and i want Alan to have some adventures. Both of your cages look like an amazing adventure playground! I feel so guilty that Alan's not had as much to do.
Just to check: it looks like your floor space is mostly covered with toys/hidey holes. Is that ok to do? I was concerned that we've taken up a lot of space and thought he'd need lots of free space for running, but actually if it's more about hidey places and the wheel is fine for the running then I'll bear that in mind for what to put in!
Will transition carefully as you suggested so Alan's a little less stressed by his big move.