Like KTM rider said, you can always reduce the output of the boiler. Even a hand load boiler will have a forced draft control system available. All the stoker boilers [recommended] will have some way of controling the BTU output.
With domestic hot water load, I'd go with the 100K BTU minimum. It is pretty easy to pull down the water temp in a boiler system with a load or two of laundry,and a hot shower with the house calling for heat.
I'm really envious.. a 14-1500 sq ft house, pluss the warm floor basement, new construction... heating with coal... Your cell phone bill will be bigger than your coal bill...