Its working great
SO far I've seen my electric bill fall $50.00 but I'm not finished with the hot tub part yet. Hmmm coil between the firebox and the jacket.. I don't think it would pick up much heat. Some people on here have done homebrew style external water coils on the outsides of their stoves, but I can't vouch for it's success..
I don't think a circulator would add any benefit since the preheated tank is close to the furnace and raised up on blocks to accommodate the water's natural convection thru the coil. I'm on the team that thinks that a circulator would mix the water in the tank, instead of letting it naturally stratify (cold on the bottom, warmer as you go to the top of the tank). This would be a negative effect since, as soon as you introduced cold water, instead of it settling at the bottom, it would mix with all the water in the tank while your using hot water. SO the end result would be that the temperature of the water taken from the preheated tank would immediately start to fall as its mixed with the incoming cold water. Not the effect we are looking for