You only need to run 120v to the boiler. It should have the Ranco aquastat already wired up. It controls the temperature of the water in the boiler which does not have anything to do with your house thermostat.
You will get continuous hot water flowing to your house. If you have it plumbed direct to your baseboard heaters and you want to control the temperature with a thermostat you will need additional controls in the house. Either secondary pump(s) or zone valve(s).
Assuming you have all your baseboard heaters in one loop, I would use a pump to control the heat. Run the pipe from your OWB to the domestic water heat exchanger (side arm, plate, etc) then put 2 tees as close together as you can get them. Put a pump in your baseboard heater loop and use the two tees as your supply and return and control that pump with your thermostat.