Floor plan planning shortly before submitting the building application

. Whether one actually does not want to heat some of these rooms afterwards is, in my opinion, a private matter. I wouldn't make a big deal out of it.

Apparently, everything lies within the heated envelope. So far so good.
However, the heat from the two heated rooms will transfer to the other unheated rooms. That means, to achieve the desired room temperature in the two rooms with heating, you have to turn the thermostat quite a bit. This is more of a comfort issue. If it goes badly, the intentionally heated rooms are too cold.
If you are already installing heating in the basement, you can also do the rest, I think. This gives you more options. As far as I'm concerned, you can skip it in the heating room.

By when do you have to inform your contractor where you want water pipes and sockets in the kitchen?

That will happen sometime in the next few weeks. The contract signing is planned for Friday next week, and then phase 4 can begin, where such things need to be done.

I need to start soon and look for a kitchen retailer I trust.

What might the rear garage door (electrically operated) approximately cost? Are € 2,217 realistic?

You can directly check the price of the gate on the Hörmann page. Then a simple motor (why actually? How often do you want to open the gate).

Let's put it this way: I have already seen individual gates for this price. Like a swing gate - which I would consider sufficient here - I don't know if it would fit visually here only in a large rib and then be priced accordingly. Electrically, well, it's usually not necessary - on the other hand: mini excavating is addictive, then you might use it daily

How much does the rear garage door (electrically operated) approximately cost?

Is € 2,217 realistic?

Could be about right.