Firstly Siberian is a name given to dwarf WINTER WHITE hamsters (these differ from Campbells and I'm not meaning to shout at anyone ).

Dwarves are social animals (in most cases) so it is actually better to get 2 of the same sex. They may in a rare occasion not get on and fight to the point of drawing blood and have to be separated but as I said this is rare; some amount of squabbling is normal. They should be provided with 2 houses so they can get away from each other if need be (by houses I mean plastic houses/nests they sleep in).

The cage you posted the picture of isn't really suitable for dwarves - it is very high and a hamster could get hurt if it falls from the top level. Dwarves are not as good climbers as syrian hamsters, being smaller and often rather rounded. Also the wheels in that picture are runged - these can break a hamsters leg (as I'm sure you know from previous hamster ownership). I personally think that dwarves are best kept in a glass tank (10 gallons minimum), if not go for a cage which is not as tall.

Finally last week a friend of mine in the U.S. found out that her 2 dwarves had diabetes, this is unfortunately too common in petstore dwarves. Hers were from where you are planning to get yours from - and she is not the first to get dwarves with diabetes from there.

Good luck and have fun being back in the world of hamster ownership