Mod com boiler questions

Tom Sherman

Hi All,
Was hoping for some advice. I am in the early stages of having an addition built and am replacing an oil furnace with a new mod com boiler.
*I've read som stuff here that talked about the loss of efficiency when used with baseboard radiators. Is this the only setback or are there other problems as well using baseboards.
*The contractor is recommending an on-demand water heater. Is this a better option than a domestic tank off the boiler?
*The house is served by a water well. What concerns should I have as far as water treatment to protect this new equipment? Softner? (The water is somewhat hard. Thanks so much for any advice and recommendations. Tom Sherman