Hinterland development - What approach? Experiences

Hello,
We have the opportunity to build on my parents' property.
It is a backland development. I now want to know how to legally approach the whole thing best. I have already spoken to the city and the building authority and have also received verbal approval that I am allowed to build on the property. The property only needs to be subdivided, and a private path still needs to be laid over a neighboring property. Everything has been discussed with the neighbor, and there are no objections, but how do I proceed now? Should I look for a contractor with whom I want to build and who will take care of everything for me, or should I first subdivide the property and arrange the private path with the building authority?
Does anyone have experience and tips on how to proceed best?
I am afraid that if I sign everything with the notary now, the city may later say I am not allowed to build? Or does the construction company do everything for me and also take care of the access to the property?
The development will be 437. There is no development plan here if that is important.
Thank you very much for your tips and experiences!

the city then says I am not allowed to build

Regarding the fundamental buildability of the property, I would trust the oral statement of the building authority in your case. For safety enthusiasts, a preliminary building inquiry is recommended.

Everything has been discussed with the neighbor and there are no objections

You can probably better judge how certain this is with the neighbor. I have experienced several times that the signature ultimately was not given when the plan including the encumbrance area was actually on the table.

that I now sign everything at the notary

Since it is your parents’ property, you do not initially need a notary contract. Not for the entry of encumbrances either.

how I proceed best?

The procedure essentially depends on what you can and want to do yourself. My suggestion: Visit a publicly appointed surveyor (öffentlich bestellten Vermessungsingenieur) near you. He could take care of the entry of the encumbrance, the subdivision (which no one else can do anyway), the site plan (which no one else can do in case of encumbrance either), the building staking out and building surveying (no one else can do these either). He will also be able to advise you on how much can be saved by utilizing synergy effects and what risk and time loss is involved. Because the encumbrance entry, subdivision and site plan could be processed simultaneously with the risk that without development no construction would be possible and thus subdivision and site plan would cause useless costs. If time is not pressing, I would
1. Have the encumbrance entered. As soon as this has been done
2. Go to the notary with the neighbor and have a mutually consistent easement extended by financial aspects entered for the benefiting parental property and the encumbered neighboring property
3. Have the subdivision carried out. In parallel
4. Consult a contractor or architect and discuss planning
5. Building application, building permit, building staking out, start of construction, moving in, building surveying

Or does the construction company do everything for me and also clarifies access to the property?

Depends on the construction company. Often they work with a surveying office. However, they also charge for these coordination tasks and if your neighbor then says "No," you will be where you are now, just poorer.