He looks lovely
I am sure he will love the Barney cage. Make sure you have a big bag of substrate ready to fill it up! I would try and fill the base of the Barney to the brim as it cushions any falls from the top if Brian decides to monkey bar along the top. Syrians are good at climbing up but not good at getting down and tend to just drop. Plus the deeper the substrate is, the happier they are because they can move it around, build mountains, burrow and sometimes dig tunnels.
I would recommend setting up the Barney with the substrate, wheel and a few toys when it arrives and letting Brian have a play in it a day or two before moving him in. This will help him adjust to the change quicker. Then when you move him in, don't clean out his old cage first. In fact if the base part detaches, you could put the base part of his old cage (open at the top, just the base) in the middle of the Barney on top of the substrate and let him explore out from there, leaving it there for a week or so until he is settled in. Is his nest in the base part?
If you don't have many toys for the cage, egg boxes, tissue boxes, kitchen roll inner tube slit down the side, all make good floor toys so it's not too open and empty. Plus a sand bath (old ice cream plastic tub maybe with Chinchilla bathing sand in). You could maybe put his food bowl and a chew or other toy on the shelf. A toy in the corner on the shelf can be good so it doesn't feel too open - a little cardboard house maybe.
Did you manage to get Pets at Home to agree to a refund? If so don't bother with putting the old cage base in the Barney, just take the old substrate out and sprinkle it on top of the new in the Barney so it smells a bit familiar. And put a big pile of torn up white toilet paper somewhere in the cage (not inside the house) so he can take it and build his nest.
Sprinkling some food on the substrate and hiding the odd treat can also distract him from feeling nervous and enjoy foraging a bit