Sounds like you are on a good path to energy independence.
As for space heating and for warming batteries, etc, I would firstly aim for increased insulation and attention to air infiltration to reduce energy losses. And for the actual heating I would aim to use biomass directly.
In theory if superinsulated, (R60), a home might need very little supplemental heating, but I think in practice for comfort in temperature fluctuations at least, a small airtight stove would fit the bill ideally.
Also nothing wrong with a dump load, but that will heat 12 hours out of sync with the greatest need, and winter solar won’t likely have excess capacity.