ᐅ Solid construction or timber / Borehole or trench collector

Hello to all building experts, and thanks in advance for your support. I hope I’m posting in the right subforum with my questions.

We are currently planning our single-family home and would appreciate some assistance. We already own a plot of land, and I have a few questions about it. I’ve attached some pictures of the property and our plans. The marked stream runs underground in a pipe about 25-30cm (10-12 inches) deep. However, the land slopes down from the street about 90cm (35 inches) toward the middle and will be leveled at street level with fill.

We intend to build a single-family house with two floors, no basement, a knee wall height of 1.60m (5.25 feet), and a roof pitch of 38°. The residential area is very quiet and not on a main road. The site elevation is 540m (1772 feet).
We don’t plan to apply for KfW funding, but we do want to achieve at least the KfW 55 standard regarding energy efficiency.

We will only have the shell construction done professionally: foundation slab and roof. The rest we will do ourselves, as my father owns a carpentry/joinery business specializing in windows, and we also have a plastering company in the family. So we will handle floors, windows, doors, stairs, installation layers, roof insulation, non-load-bearing interior walls, interior plaster, and possibly exterior plaster ourselves.
I will take care of the electrical work; I’m a certified master electrician and work professionally in this field.

Currently, we are still undecided between timber frame construction and solid masonry.

For timber frame construction, I have concerns about sound insulation inside the house (children’s rooms above the living room with home theater). Is good sound insulation between floors achievable in this system?
With timber frame construction, we can do much ourselves since only the stud frame with plaster carrier board (or wood fiber board with an air gap and wood facade) would be installed by the builder. We would take care of wall insulation and cladding ourselves. We already built my uncle’s house ourselves this way about 10 years ago. What bothers me there is that when the children play upstairs, the noise is clearly audible in the living room below. However, his house has an open beam ceiling with ventilation ducts running above the visible boards.

1. Are there any experiences with other floor constructions here in the forum? We don’t need an exposed beam ceiling and have also considered a cross-laminated timber (CLT) ceiling.

2. As an alternative, solid construction is also an option—only the outer walls and load-bearing walls. However, I would prefer to avoid external thermal insulation composite systems (ETICS / external wall insulation) and build monolithically if possible. Or do you think there are better alternatives currently?

3. We plan to use a heat pump with geothermal energy. Given the lot size, I considered trench collectors, but I wonder whether they have to be placed directly next to the house or, as in the drawing, can be a bit away from the building? The piping would then connect in the garage approximately.

4. Heat distribution is planned via underfloor heating throughout the rooms, and a stove with a water jacket in the living room is intended to support heating. I thought the heat from the stove would be fed through a mixing valve to both the underfloor heating circuit and the hot water circuit.

5. A central ventilation system is not planned; instead, decentralized ventilation will be used in the living area, kitchen, bathroom, and possibly bedrooms.

Maybe you have some additional ideas?