Alby's Linnmon cage is amazing! He is a lucky hamster
Kirsty - 30cm deep is a bit narrow really. 100 cm long is great and so is 40cm high. Ideally it would be 45 to 50cm deep for them, but if you set it up carefully 30cm deep may be ok. Or you could make a bin cage or the Linnmon cage! For a pair of dwarf hamsters you need enough floor space for two of everything. Two houses, two wheels, (some owners of pairs even put three wheels in), two food bowls and water bottles - so they don't get territorial over anything. They may both sleep in one house together or run in one wheel together but you always need another one so they can have one each if they suddenly change habits or one gets territorial. No levels for the same reason and any floor toys like tubes need to be large enough to fit them both inside easily.
I would go for something a bit deeper if you're having a pair, but the tank may be ok for one dwarf hamster - and also then you wouldn't need to worry about set up issues or two of everything.