The traffic from the main road really bothers me
If there is still room in the budget, one could also plan a sound-absorbing wall / fence / planting or the like there.
What if we rotated the house 45° clockwise? Then at least the living rooms would get a good amount of sun.
You mean based on your last sketch from post 54? 45 degrees is "crooked," you could also call it diagonal. By rotating like that, your house would move even further away from the northern property line overall, and thus your garden towards the south would become smaller or shorter. And if you then want to build the garage parallel to the house, you would lose space in the north due to the crooked driveway, which you will miss on the south side.
By the way, I noticed that you planned the double garage there with a boundary distance. I would give that up in favor of a larger garden to the south. And I would also consider placing only a single garage to the north to make more space for the south garden.
If the budget allows, one could place a second single garage in the shaded area by trees along the southern boundary, which would fulfill a sound protection purpose if both cars must not freeze during winter.
I would try to extend the kitchen area all the way to the southern corner (with west-facing windows and close to the entrance), move the office away from there and assign it to the north side. Or do you spend a lot of sun hours in the office, so that the location there is important to you?
By the way, I received a rough-shell offer of 80k euros today to get a rough financial direction. Of course, a few things still need to be added and deducted but the direction is right.
Since I am professionally involved with earthworks: Where and why should the 29 cbm of foundation excavation be stored? Do you need them? Otherwise have direct disposal offered. Is the soil beneath the topsoil stable or does it also have to be removed? Topsoil and frost protection are offered per sqm, is it known how thick the layer to be removed and reinstalled is? Try to find out how deep it has to be and agree that the price applies up to that depth. You don’t want extra charges later due to larger volumes...