Trying to plan and build an off grid home, wish to use most 12 volts, one small 120v circuit,,would have generator for back up and couple large items ..any thoughts would be helpfull

That's going to be some pretty fat wire if you have any 12V loads with high startup or peak power requirements. You end up paying a premium for 12V versions of standard stuff like lighting too. Higher distribution voltage=lower current for the same power, ergo thinner wire. (A single 100W DC ventiltation fan or pump motor can have peak draws in excess of 10 amps, at 12V.)