Heating for old buildings (previously only wood single stoves)

It's all a question of money. Ideally, you would completely tear everything out, insulate, install new windows, cut channels in the screed for underfloor heating. Then calculate and install a suitable heat pump (sounds like a large property, so as a ground source heat pump with a horizontal trench collector). While at it, install a decentralized ventilation system with heat recovery. (All buzzwords you can google)

You probably don't want to or can't do that.

There are water-bearing wood stoves. They heat the room they are in directly, and indirectly a storage tank in the basement with warm water.

There are pellet stoves, with which you could replace the wood stoves. But pellets cost money and are worse in terms of CO2 than wood.

There are log wood boilers that burn large amounts of wood at once, transferring the energy to a storage tank in the basement, from which you can then draw.

There are ceiling heating systems in drywall construction. Warm water is pumped through a suspended drywall ceiling. Basically like underfloor heating, but without cutting channels in the screed. Can be done with sufficient room height and no stucco.

All in all, quite a lot of work and mess, because you really won't avoid centralizing the heating supply.

Hi

If you want to continue heating with wood, a wood gasifier or pellet boiler in a boiler room would be possible.
A buffer tank with domestic hot water preparation as a hygiene storage tank or with a fresh water station suitable for the system size.
If desired, and to avoid dealing with the wood heating system in summer, an additional collector system.
Subsidies are possible for this, e.g. from [BAFA] Pellet boilers up to €5750 Combined boilers from €7500

Olli

Completely renovate or leave it as it is. My opinion. For example, older, only moderately airtight windows harmonize wonderfully with decentralized fireplaces in terms of ventilation, indoor climate, thermal comfort, condensation prevention, etc. If you install a more modern heating system now, you will A) have to operate at high flow temperatures, making the heating system uneconomical B) still not have a comfortable indoor climate C) possibly get mold problems, for example in the window reveals.

This applies not only to the windows but to all components: floors, ceilings, exterior plaster, interior plaster, insulation materials, etc. So if you additionally seal everything, insulate inside and outside, and whatever else: you will suddenly have problems with rising moisture in the masonry, which was previously able to dry unnoticed and was heated out by the stoves. So complete drying out, which then causes other problems again.

If I have read correctly, you are also considering a wall heating system. It has the advantage that it can often be installed on the exterior walls with internal insulation without problems with condensation. The top floor ceiling is usually easy to insulate. Depending on the windows, new sealing and glazing is possible and relatively inexpensive to implement. This already makes it possible to lower the flow temperature, at least with continuous heating. The advantage is that you can flexibly choose the future heat generators.