Evaluate the boilers by calling the suppliers in the area and find what brands they have been selling for the longest time. Suppliers are conservative and do not take the ‘latest’, but choose the most dependable for their confidence, as installers will buy more units if they have less trouble. Major boiler companies will help lay out systems in cooperation with the supplier. That way you will get a heat loss estimate to get the right size system as well as a good design.
Use pex for radiant floor heat. Utah is a great place for concrete floors with warm tubing inside. Otherwise connect the hot water radiator and system with copper. Insulate the tubes. Floppy plastic tubing eventually gets tired looking unless encased in flooring. Ducted systems are nice for upstairs rooms when air conditioning is needed.