If you're looking to get the correct thickness for the cards, ask the print shop to print them on 14-point paper, or whatever they have in stock that requires a printer drum to have a rating of just over 300 psi. Through some experimentation at my job and a bit of research, I've discovered that to be the thickness of all trading cards. If they don't have a machine with a drum that can handle it, they'll know someone in the area that will.
Keeping in line with ikegami's comment, I would recommend not printing a back on the cards unless you expect them to be unsleeved for any great length of time. The price of the paper is, relatively, marginal; it will generally cost a dollar's worth of cardstock to print a large number of cards. However, tonor is really expensive, and it'll easily be 80-85% of your total project cost.
My one other recommendation would be to cut the cards yourself. Unless you personally know the person cutting out the cards, you'll most likely get unseemly white edges and the occasional slanted cut, especially if their cutting machine is slightly off.