Here's some more.
Ohm's Law Calculators has a calculator for figuring out total power requirements. I don't know what the "% over peak" standard is(mabye 20%)? Bigger is always better for future needs.
American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies has some info on resistance drop over distance.
There is a difference between interior-rated and exteriour-rated wiring. Some can be directly buried and some are required to be enclosed in a conduit. For safety, I'd recommend the conduit anyways.
Better double-check wire type and burying depth with the city before buying anything.
+1 on telephone/cable or leaving a sacrificial pull-wire for later needs.