I probably can't help much with the belt selection, but a good start might be a 10 or 16mm HTD belt with a 5mm pitch. That is a fairly universal pitch. For the calculations I recommend that you go to this site http://www.sdp-si.com/Cd/default.htm
This is a handy Centre distance finder and also allows you to play around with different pulley combinations. Very handy.
Hope this helps.