Here's a good cost comparison of water heaters including initial cost, fuel, maintenance, etc. I've queued it up to the comparison chart:
https://youtu.be/wt95SE2ogNI?t=625
Also, here's another one discussing the pros and cons of tankless:
https://www.youtube.com/watch?v=8RFuFBI3r2c
Caleffi provides a good discussion of Legionella and domestic hot water in Idronics 22:
https://www.caleffi.com/sites/default/files/media/external-file/Idronics_22_NA_Safe%20and%20sanitary%20hot%20water%20delivery%20systems.pdf
Our new house (off grid, primarily solar electric with some propane appliances) will have radiant heat from a wood gassification boiler. There will be about 800 gallons of hot water storage which will run from about 120F - 185F. This thermal battery will heat the floor and will also preheat the domestic hot water. In order to make it as seamless as possible, the stored hot water will be pumped through a heat exchanger to preheat cold water going into a traditional tank-style propane water heater. If there is stored heat from a fire it will reduce (or eliminate) the use of propane. In the summer, propane will heat the water or we could light a fire as needed. The output of the propane water heater will go through a mixing valve to provide a safe temperature at the fixtures since the boiler output can be far too hot for safe use.
The heat storage tanks and a bunch of pipes need to be fully insulated and then the heated floor will be fully operational. Performance of the domestic water preheating won't be known for a while yet. So far, the boiler is working great except for one last leak in the piping. It's not a rocket mass heater but the burn chamber looks plenty hot to me as you can see below.