Your are on the right track.

Go with the dealer that seems to know what they are doing.
Especially as you will need to add ducting and controls.

Contact your local electric utility company and find out if there are any rebate programs they offer. Some require you to use a "certified " dealer. Some might offer programs on Heat Pumps but not AC. Find out so you are aware of how this might factor into your design.

I would look at Heat Pumps, because as you now know., it is tricky with hot water to keep the house heated in the spring/fall when the days are warm and nights are cool (but not cold) My house has radiators, and we put in a heat pump last May. We love having the house warm in the spring/fall when it's cool, but by the time the radiators kick on and heat up the house, the night is over. Now we have the heat pump.

I agree with previous post 100%. Heatpump shouldn't cost much more than regular A/C. Heat pump heat is also comfy and efficient when not terribly cold. Ofcourse if your electricity is expensive heating with a heatpump isn't as much of a deal, but its certainly much cheaper (1/3 of the cost) than heating with straight electric.

Julie and neo, I have no clue of what the hell your saying. You can control boiler temp with an outdoor reset. That ables you to control the water temp bassed on outdoor temp. When and if it is designed with a J-manual it only meets the max but loss 15% of the time, that would be the whole concept behind this outdoor reset. Radiant floor is the 2nd best form or heat next to steam when done right........
As far as the question is concered since you live by the dhore you will only get about 10 years out of a unit becuase of salt air....... You really can go with any unit I install everything from goodman to carrier....