we have just built a new guest house, 600 sf with extra insulation R19 walls, R38 roof, and rigid under concrete, small windows, trellis on south side, overhangs. The pex tubing is in the concrete slab and ready to be hooked up to some type of heating unit. (circuits are ~280 lf, 1/2"). This summer the house has been very comfortable despite the heat outdoors without AC.

the question is what heating unit would be the best? The plan is for the system to have solar thermal panels to provide backup heat into some type of storage tank (maybe superstor but very expensive, others?) and also to allow all excess heat from the solar panels to dump to the pool to provide some heat there. The heater for the house radiant and DHW should also allow for some occasional heating of the pool heating manifold (i have 1300 lf of pex in the pool shell).

what heater makes sense?

-sm mod/cond boiler (though i've been told that a condensing boiler requires expensive annual maintenance that doesn't justify the 10% increase in efficiency over a mod boiler)
-mod boiler
-tankless water heater ?
-high efficiency water heater?

We're in northern California. the climate is very mild. Not that much heat is needed.

Also, is an outdoor reset very important? I've heard differing advice.