Initial ideas for building a small house on a backlot

I quote directly from the communication with the real estate agent: "The property must be developed as a rear development. For this purpose, a building encumbrance has already been registered that ensures the development."

Aha, so all clear. No building encumbrance for you, but in your favor: namely the right-of-way corridor of the front property owner. So the next step for the homework (which I already mentioned): is this a complete "right of way, access and utility easement"?

This plot of land is about 50% too large for that.

Would it be possible according to the development plan to build a two-apartment house there? Then, theoretically, one could join forces....

Is this a complete "right of way, access, and utility easement"?

How do I find that out? Ask the real estate agent?

Would it be possible according to the development plan to build a two-apartment house there? Then, theoretically, one could join forces....

The development plan says ED.

How do I find that out? Ask a realtor?

Better read the land register sheet (or here: in some federal states the separate register of encumbrances) yourself.

The debt service alone makes it a luxury to put a summer house on a standard single-family house lot. For that, this plot is about 50% too large.

What size must a house have to be allowed to stand on a 500 sqm plot?
A 170 sqm house with 2 floors does not have more ground area than a bungalow with 100 sqm.
A plot is open space. It cannot be too big.

Land is open space. It simply cannot be too large.

I agree.

What size must a house have to be allowed on a 500 sqm plot?
A 170 sqm house with 2 floors does not have a larger footprint than a bungalow with 100 sqm.

I would love to have a cabin in a park myself, so I can understand it. Only the business sense is, if it is only about avoiding the expensive renting of a moderately small apartment, at least questionable. Using a sledgehammer to crack a nut.

Would it be possible according to the development plan to build a two-apartment house there? Then, in theory, you could team up....

Then you just lose all privacy. And don't underestimate what things like a garage, garden house, etc. nibble away from the property. If you want a small house, I would aim for about 90-100 sqm; there are also several standard floor plans for bungalows in that size. If you go even smaller, the floor plan has to be very well planned. There is a corresponding subforum here. Building small and then adding a basement is financial nonsense. Even a small basement has high fixed costs.