ᐅ House electrical rewiring, cable cross-sections, and related aspects

Good evening everyone.
First, I would like to briefly introduce myself and explain my project in order to get the necessary knowledge and tips from you.
So, my name is Marco, I am 29 years old, and I work as an automotive mechanic with several additional qualifications, including high-voltage systems in vehicles.
Since I bought a house from 1958 and the electrical installation is correspondingly old, I would like to gradually renew the entire electrical system in the house—not all at once, but step by step—with the primary goal to start with my main rooms (living room, kitchen, bathroom, office, bedroom). As I am quite a tech enthusiast, I want to keep some options open for possible future upgrades. If you are still reading this text, you’re almost done J

Currently, the house has a main distribution board with the meter and about six circuit breakers. My plan is to install a sub-distribution board with three-phase power on each floor. The first floor contains the living room, kitchen, office, and corridor. In the kitchen, obviously, there will be a stove and a small tankless water heater, etc. My questions are as follows:

1. What cable cross-sections are required or prescribed for: stove, small tankless water heater around 10 kW, lighting, sockets, riser cable from the main distribution board to the sub-distribution board? Also, the riser to the second floor from the main distribution board to the sub-distribution board. (Here, later on, a tankless water heater with about 30 kW and an air conditioning system will be installed. Maybe solar energy on the roof even later.)

2. What minimum distances should be maintained between different cables such as power, network, satellite, etc., to avoid interference?

3. Where should or must empty conduits (cable ducts) be installed?

4. Is it allowed to combine high voltage (230 V) and low voltage (12 V...24 V) in the same distribution board?

5. Any further tips or points that I should pay attention to according to standards (such as VDE, etc.) when installing and connecting cables? So that I can, if necessary, get the important certification stamp from a licensed electrician for my work...

You don’t need to lecture me about working on live electrical systems, etc. J As mentioned, I have additional training in high-voltage systems on vehicles that sometimes involve over 20 kV. I am well aware of the risks and safety measures—even though the two things are not exactly comparable J For assistance, my grandpa, who is an electrician, is available. But he is not familiar with current regulations; he stopped somewhere around 1970. His attitude is “Two circuit breakers per floor are absolutely enough. What else would you want to connect there?” Following that mindset, I am looking for answers from experts or people who really know their way around this and can answer my important questions.

Thanks in advance! J

Writing all of this out in text form might be a bit difficult and could become confusing. If you have a floor plan, you could send it to me, and I can plan the entire project for you. I will then share the important points you should consider here so that everyone can benefit from them.

That sounds great. I’ll send you a link via private message soon where you can view the floor plans. Thank you very much in advance :-)