Does anyone of you know how to proceed here? Do you need an architect for the setup or "only an engineer/civil engineer?
Uff. You can ask questions :-(
I'll dabble a bit by throwing in some scraps of thoughts: it might be worth considering handing over the street to the municipality after its construction and dedicating it publicly # you’d have to ask how far the street would be attributed as a secondary facility to the built-up areas or whether it makes sense to mark it as an independent plot # as a purely private road, it only exists publicly as a driveway: for connection fees to the public road in front, for "sweeping meters" of a street sweeper etc., you would probably all be treated as if the properties were all located on the road # I assume the houses will be in a row and the property on the public road wouldn’t really need the private road?
And two more general thoughts about such a community of fate of builders: firstly, I would recommend finding a joint architect and joint contractor (for the houses, I mean); and secondly, I would consider a shared house connection and heating center, e.g. installed in a fourth garage.
By the way garage: think about creating parking spaces/garages together, at the public road. And then manage with narrower driveways or even sidewalks going backwards. For example, 3 m wide, enough for moving vans and ambulances, with posts to be locked, only serving as a sidewalk in everyday life. Just some advice-slaps ;-)
And I would think towards a property developer, they have experience with the overall situation when they place residential complexes on old industrial brownfields, etc.; and basically, their business also works organizationally the other way around with the house buyers from the start as clients.