If the 170m2 includes the attic room, and it is inscribed as such in the register and the tax forms, then I would be a bit more confortable. But would advise to do the homework and really check the official commune/tax records on this, especially if these figures just come from the realtor.

Now that you give the m2 for the ground/garden etc., it is not exactly a huge space considering the pool space. As such, really do your homework with the geothermal guys who will drill for the heatpump. You may only have one available space to drill, and it may not be suitable. Some communes limit it further, also due to noise factors from the heat pump. So try to get firm commitments from them that it is possible before going the heat pump route.

Otherwise, not sure if you need/want an architect, maybe a general contractor or engineer may be more suitable. Good luck.

Assume this one that lasted for years had underfloor water heating? As I understand only certain types of wood are suitable for underfloor heating, and then it does not always go as planned.