Start your search here for the voltage drop calculator - www.ifigure.com/engineer/electric/electric.htm
Add all your loads in amps or convert from watts to amps. Formula for this is P (power) divided by E (voltage) Add an extra 50 amps for incidental loads. Minimal burial for conduit is 24 inches in a sand lined trench and sand above the conduit. Earth loam can finish off the trench.