Tankless hot water is nice because it only has to keep three or four gallons of water hot ALL the time...which also likely supplys hot water for baseboard heating. With a seperate 60 gallon hot water heater, (as an add on to the tankless if you want,) you have to keep 60 gallons of water at 180 degrees ALL the time, so it's going to be more expensive.
There are "Upper' and "Lower" temperature limit switches on the furnace inside a little tin (Honeywell) box, that can be adjusted (within limits) to adapt to your showering style. We keep our lower limit at 140 and the upper limit at 180 degrees. That's probably as low as you would want to go. You can raise both limits to say 160 and 200 respectively, using the little adjustment knobs inside the box.
When the water temp drops to 160, the furnace will come on for as long as it takes to get the temp up to 200, at which point the furnace will go off. If you are taking a shower during this cycle, it will take longer. I don't think I would raise the upper limit beyond 200. (Don't want the water to boil.
) NB
EDIT: Set the upper limit
"at least 20 degrees above the lower limit."
EDIT 2: I think I would use the system
As Is for awhile until you become more familiar with how it works.