There's a list of cages on the forum, suitable for a Syrian, although to be fair not many of them are available in the US, which is why a lot of US owners use detolfs and tanks.
It comes from a welfare minimum really - as Beryl mentioned - Syrians need at least a 10" wheel - ideally 11" or bigger - to run properly so a cage needs to be able to fit that. Many modular cages are sold with a wheel that is far too small meaning a hamster can't run with a straight back and that can lead to pain and back problems for them - or frustration and pent up energy if they stop using it because it's uncomfortable.
So the main cage needs to be able to fit a Syrian sized wheel - add-on units are fine for extra enrichment, but it's better to get as big a cage as you can - and at least 80cm by 50cm.
Pet stores sell these things but it doesn't mean they're suitable. I'd suggest finding something else for Dash and taking the others back for a refund because you must have spent a fair bit of money on all those things. Even if they've been used. We've had hamster owners do that before - returning them and saying - this isn't suitable for a Syrian hamster.