As far as buying dirt goes, I'd go to a landscaping company(call first) and just get screened black dirt, add in some bark and leaf litter, and a little bit of organic compost... Nothing acidic! Lettuce and carrots n potatoes and good. No apples, oranges, tomatoes etc.

Don't put them in the fridge if you want them to breed... Fridge is great for keeping them alive, yes. but in a sleep state. Find a cold spot in your house n keep them there, they will breed at room temperature or slightly cooler.