It would be nice if they let you reserve her - if she seemed to be the one for you
But even after the cage arrives, you'd need everything set up and in place first, so you don't need to start changing things too much after she goes in there. So you'd need the substrate, wheel, house, any access sorted (ie how to get up and down to things) with bendy bridges or ramps. It can be a bit of a fiddle but as long as it's more or less ok to start with you could add the odd thing later - but they don't like things moving or changing too much when they get used to a set up, especially while settling in.
It's a tricky one - seeing the ham prompts you to get the cage. But then you have a cage and need to find a ham! Hope your cage comes quickly
Sometimes it can be 2 or 3 days from ordering, other times a week.
Meanwhile you could plan the cage layout. The white house that comes with the Alaska isn't any good as a nesting house really and the holes are too small for a Syrian - one that grows large could get stuck in the holes. It's easily removed though and you still have the shelf. A shoe box on top of the substrate makes a good hide/ house - just turn it upside down and cut a hole for a door. Maybe partly under the shelf. A bendy bridge or two is handy - they can make a ramp or bridge to get up to a shelf and a hide/toy for the cage floor as well. And you'd need a bottle, food bowl and some food ready to go (I'd suggest starting with Harry Hamster - Tiny Friends Harry Hamster). You could maybe get a little bit of the mix the pet shop is using and mix it in with the Harry Hamster at first - so it's a gradual changeover.
Did you order a wheel from Zooplus with the cage? If not, the Trixie 28cm wheel is available on Amazon and is about the cheapest syrian sized wheel - most people seem very happy with it. If you don't mind paying a few pounds more I think the 27cm wodent wheel is better because you can hang it from the top bars - it's more stable that way and you don't have to worry about the wheel moving around or falling over or not having enough substrate in the wheel area. You can only get them online though and the only stockist I know that has them in stock is the sugarglider shop
11" Wodent wheel (27cm)
11" Wodent Wheel (Senior) & Free Glider Shield
They also sell the 12" Silent Runner which has a bar attachment so you can screw it to the bars, but that works out a bit expensive - it's about £24.99 with an extra £4.50 for the cage attachment (and it seems to be out of stock).
You just need about 3 cable ties to secure the stand of the wodent wheel to the roof of the cage. You slot the stand through the top bars and then attach the wheel to the stand inside the cage (or with the cage top off) then put 2 or 3 cable ties at strategic points so the stand doesn't move. They spin better upside down I reckon
Then you just need something like a couple of cardboard tubes for toys - a kitchen roll inner tube can be good, but best to slit them down one side so they expand. And lots of torn up sheets of plain white toilet paper in a big mound on top of the substrate so the hamster can take what they need to build a nest with.