I'd go with the boiler,, use a water to air exchanger for the FA Plenum like you describe, and either use an indirect hot water heater/tank,, or use a water to water plate type heat exchanger in the cold water supply to the DHW tank.. this will provide you unlimited hot water..
The Forced air furnace can be equiped with a DHW loop, but this is a low btu coil that takes time to preheat a tank of water, with this, you can run out of hot water.. with the boiler system described above, you won't run out..
A furnace isn't as long life as a boiler,, 20 years is easy with a boiler,, many are going strong after 50years.. a furnace is more prone to corrosion issues and cracks.. I recommend the boiler system..
And as Lumberjack suggested,, install hydronic floor heat in a few areas,, like the kitchen and bathrooms,, from under the floor if you have basement access to these floor areas.. you will really like the warm floors..