most important thing is drainage, partly for keeping your basement/foundation integrity but most importantly for the septic/leech bed. I'm assuming you'll have access to a municipal water supply, if so you'll need to get a price for running the line to your home and the tie in costs. If not, you'll need to price a water well. Getting power and internet to your property are also things you need to be ready to account for. something i've heard others mention is to have an inspector look through the house while building is ongoing to make sure things are done correctly and can be fixed before being covered up by walls.
all that said. congrats. happy building.