1. boiler + indirect tank for radiant system, with separate water heater for domestic hot water

2. high efficiency and powerful water heater like a polaris, or bock, for both domestic hot water and radiant system (through a wall mounted heat exchanger).

3. tankless water heater for radiant system, and regular tank heater for domestic hot water.

4. two separate tanked water heaters, one for domestic and one for radiant

Am I missing any choices? I like #2 the best since it's the simplest and probably the most cost effective (after including all labor). However, I am worry the polaris 50 gallon will not be strong enough to provide a radiant system of 4000 sq ft. It will be separate in 4 zones, 2 1000 ft zones, 1 14000 ft zone, and 1 600 ft zone. In addition domestic hot water needs is for 2 adults with 2 kids with a bathtub in master bedroom, and I can imagine having 2-3 showers running simultaneously. Does a radiant system normally cycles on and off alot? Meaning do I have to worry that I can't have both domestic and radiant drawing water at the same time?

Lastly, instead of a wall mount heat exchanger, can I connect an indirect tank (which has a build in heat exchanger) to the polaris? If so, is the extra tank capacity be useful for storing some heated water? What I read is that the indirect is fed from the boiler, and I wonder if it can be fed from the Polaris instead. Also want to see if the tank can be helpful in minimizing heat loss and increase storage compare to a wall mounted heat exchanger. I would imagine a simple wall mounted heat exchanger will lose heat to the surrounding, and even if it's insulated it must not be as insulated compare to an indirect tank.

You need to start by understanding the actual demands of the individual systems. In other words, if you were to go tankless for domestic hot water, what size unit would that require? What do you need in terms of BTU for your boiler, etc. I think that will narrow down your choices considerably.

This.

The boiler needs to be sized for the design limits, and the rest of the time (actually almost all the time) is oversized.

Using a boiler wit an indirect tank and a reset thermostat allows the tank to serve as the buffer between system size for the coldest hours and the actual needs of the house when temperatures are milder.

The boiler heats the tank and runs hot enough to not be damaged.

The temperature in the tank is controlled by a reset thermostat based on the outdoor temperature.

The zone valve allow final tempering for each zone based on their actual requirements.