Hey Joehvac25, thanks for your input. You're probably right, I most likely am over engineering this, all with the idea of keeping it simple. I figured I could use either a flow valve or a strap on aquastat. I assumed I may need a mixing valve on the hot side.
If I add a second water heater like you suggest, would it be parallel to the first, or in series, and why do you suggest a mixing valve? Is it for safety, and could I essentially just start with with the temp control valve in the shower set a bit colder, and push it along as needed? I'm fairly sure I mentioned having a baby in the house, so if the mixing valve is for safety, then that makes complete sense to me.
What you're saying about the boiler needing some time to get up to temp makes alot of sense, considering the amount of water that must be in there. Out of curiosity, if the plate exchanger was installed on the hot side of the water heater, and the circulator/zone controls do not start flowing boiler water until the unit is at least warm, then would it work? I'm rationalizing that the boiler would be up to temp and able to help out, if not take over, by the time the water heater was starting to run cooler. I'm starting to agree about this being unreasonably complex; if I went with a flow valve, then every time someone washes their hands its going to short-cycle the boiler. If I go with an aqua-stat where would it go? It could go on the cold water supply pipe just before the water heater, but that could also cycle the unit unnecessarily. On the hot side it may run the boiler extensively if there is no call for hot water and the hot side pipes cool off. I suppose a flow switch with an adjustable delay, and now we're back to over-engineered.