We are building a 11,000swft ICF square building.  It will have some large spaces for work and garage but all have in floor heat, buried in concrete on every floor and zoned so garages etc can not get as much heat.  Our walls are 8″ core ICF and our windows are .21U triple pane.  Trying to figure out what boiler we should be getting for the infloor heat.  Should we use the same one for the house hot water or separate them?  The house part has 4 bathrooms with showers but only 4-6 occupants at a time most of the time. 
Usually our area uses heat 9-10 months a year (PNW) with an average temp difference from the outside of just 15-30 degrees.  In the winter we may have a few days where it gets into the 20s, but not many.  We plan to use mini splits in a few rooms to help with AC on hot days, but no reason to run a full hvac for as little as we need it.
Our electrician friends beg us to use gas boilers for the radiant heat, they deal a lot with problematic electric ones.  But they said instant hots for household water work great with electric so I’m trying to figure out if we should do an instant hot for house plumbing and boiler for radiant. Or if we can use the boiler and run it for both.
We plan to have a LP tank for cooking and the boiler.  Just really not sure what system to use.  I’ve emailed companies for help and they all want me to tell them a BTU – which I can’t figure properly out based on the info I gave you.  Anyone super smart in this area??