Complete renovation of a small house built in 1973

A few thoughts:

There is simply no space for pellets in a 100m² house. That is simply out of the question.

Maybe it would also make sense to increase the living area through dormers or an extension?

Actually, everything has to be new. If there is insulation on the facade, the roof inevitably has to be redone, as there is no overhang on all sides.

Intuitively, I would have estimated 1000-1500€/m² for a complete renovation. But of course, I know too little about the house and the personal requirements of how it should eventually be.

If everything is insulated and underfloor heating is installed, the heat pump is optimal. I would contract everything separately. The [BU] is taking on a big chunk here.

Thank you for the comments. I have one more question regarding the exterior wall insulation: I was told by several acquaintances that such insulation could lead to extreme problems with mold growth in "old masonry." Insulation is actually only suitable for newer buildings (fewer thermal bridges over concrete ceilings, etc.). What is your opinion on such statements? Isn't mold growth ultimately dependent on ventilation? A central ventilation system is apparently not possible in this house. Therefore, I was thinking of a decentralized automated system on the ground floor and upper floor. Does anyone have experience with this? Thanks and best regards!

Insulating old houses is basically not a problem. It just has to be done very precisely to avoid thermal bridges. The be-all and end-all, however, as you have correctly recognized, is sensible heating behavior and proper ventilation of the building.