Tricky isn't it. I rearranged our room to fit an 80cm cage and then found I had space for a 100cm cage and wished I'd got one in the first place as I've now upgraded Charlie to a 100cm one.
On the other hand, having the cage in the same place will be more familiar for your hamster.
If he nests under the shelf I would just try and lift the nest and hoards in tact and pop them in a similar location in the new cage. But if you have room for a house in the new cage you could put the house in the same location as the nest is now and put the nest inside it - he's more likely to nest in the house then. Or if you want him to nest in a particular place, then I've found putting a bendy bridge tunnel over the house door tends to tempt them in there straight away and then they're likely to nest in there because it's nice and dark.
I would just put the new wheel in the cage - and leave the old one in the old cage. Charlie took to his new wheel straight away and didn't seem bothered about not having his old one. The main thing is keeping their familiar scent - hence moving all the substrate over.
If you're going to get him a house, you could even get away with not moving the nest and just putting a bit of his old nest in the house and put lots of white torn up toilet paper out and he'll rebuild it.
If you get the Alaska, and would like to get a house, I'd recommend getting a house with a flat roof and putting it at the end where the shelf is in the Alaska, and using the house roof as a shelf. You can always add a couple of smaller corner shelves at some point.
On the other hand - I found having a good sized house took up too much floor space in an 80cm cage, which is why I'm happier with a 100cm one. There is room for a good sized house, a large wheel and still loads of floor space.
The Alaska is 84cm though - which is almost a couple of inches wider than my 80cm cage and it does make a difference when setting up, so it should be fine.
Rodipet make some great houses. I emailed them recently to ask which houses they would recommend for a large syrian (or any syrian) and they recommended three. There was the large labyrinth one, which I got (but would take up a bit too much space in an Alaska and I'm not sure about it yet either!).
I can't remember the third one, but the second one was this one
https://www.rodipet.de/shop/haeuser/...u-talalin.html
I think it's a great house - it has two rooms - one for a nest and one for a potty, and a middle compartment for hoards. It can also be part buried in the substrate and will fit along the full depth at one end and still leave lots of floor space. And you'd have room for a shelf over it as well if you wanted, but I'd get a couple of corner shelves rather than that big one the Alaska comes with, as it will make access to the house easier.
I sometimes think you need to get the house and wheel to fit the cage.
So with the money you save getting the Alaska instead of the Barney, you could get your hammy a good house and a good wheel.
Something like these two shelves from Ranchhouse cages might be good. So if you had the wheel left back corner, the house at the right side along the full depth of the cage, and two corner shelves front and back right, you'd have a good set up and still loads of floor space for toys and tunnels and so on.
Solid Pine Corner shelf - Small Medium Large from mouse to guinea pig size | eBay
If you do get the house from rodipet, I can recommend getting one of these at the same time
https://www.rodipet.de/shop/zubehoer...a-6-10-cm.html
It's a great tunnel and floor toy, and something to climb over as well. And it's a good size for a Syrian - most of them are massive, but the Rodipet ones are the size they say they are. It works out about £7 uk money. The house costs £19.99 in Uk money and postage is £7 however big or small your parcel is.