I had some of the first siberian dwarf hamsters in florida. I fed them mainly bird seed mixes, and they thrived and bred tons. Raised full litters.
No sunflower seeds in the mix, more like finch food if I rem right. When the russian and chinese dwarfs showed up, there was a lot of interbreedings, and the siberians got very scarce. I found my original siberian stock was very tame, while all the new blood was nippier.
Aspen shavings worked quite well, as long as it was the soft fluffy stuff, they liked to burrow a lot.