I have mine in a drafty basement window without a heat mat. It is growing now. The plant seems to have a summer dormancy. I've rarely if ever fertilized my plant. If you have a fast draining mix and don't over-pot the plant then I expect you won't have problems with rot. Mine seems to thrive on benign neglect. I'm surprised you ordered plants at this time of the year. Your zone has below freezing temperatures.

Edit: Fair warning.. my experience with the plant might be atypical. By doing a Google search I found a couple other threads with some different advice.

Pls don't any sand, unless it's coarse it can make for problems, particularly w/ succulents that are prone to rot.

polypom,

you'd think--it's actually hovering around 45-55, which from what i've read they can handle for a short period when dry.