On regulating for the water heating application: the Coal-trol is not designed for this purpose nor do I believe you could hack it to be all that good at it. You'd be better off with an idle timer and the aquastat to kick it into gear when heat is called for. Even then expect delays of a dozen or more minutes before the hot water coil starts transferring much heat into your domestic tank. We've had a number of requests for a boiler control in the past few years. When we get that out, that would be a much more likely fit for this application.
As for controlling the heat output for house heating purposes, Coal-trol Digital is designed precisely for that purpose.
Mixing the two purposes (water coil and house heating) may prove a bit tricky. I could make some guesses as to how to pull it off, but I don't know for a fact and wouldn't want to lead you astray. It is done though, so hopefully someone else can pipe up with ideas for you. And hopefully you will chose to integrate a Coal-trol into your plans.
If you call the shop (315-299-3589) Neil may be able to guide you better on the details of what you're wanting to do and how the Coal-trol can fit into it.