With a 300 ltr tank youve got a little more than I beleive is specified just for solar thermal DHW. I dont think you will have anywhere near enough storage to do much space heating after a stove burn the night before.

As I see it where you go now depends on how geared up you are to heat with wood as your primary fuel. If youve got a ready supply thats cheap/free and youve got a couple of seasons dry storage capacity, then Id go for a much bigger tank to use as full thermal store for the next days heating. If you dont have the wood at the right price then go for a gas/oil boiler and use a smaller tank(maybe the one youve got??) as a buffer between solar/stove/boiler

I may hve missed it, but nobody seems to have done the basic calculation of how much useful heat you can store in a 300 litre store.
If you assume the whole 300 litres is available, and theres a useful heat range of 80 down to 40C, then thats ONLY 14kWh.

So how much do you need? I can only go by my own heating records - large detached house, reasonably insulated in SE england. I use 100kWh per day in midwinter.

So I'd humbly suggest your 300litre tank is WAY too small. You just cannot store enough heat in it.