Extension, two full floors, ~476 sqm

- In the end, of course, the financially possible framework within the family circle decides. For me, it is about preserving the existing property and building an alternative form of retirement security with such a project.

Could you please elaborate on what you mean by the financial framework within the family circle?
What will the ownership structures look like?
Is it only about your retirement?

Who stepped on your tie? But to stay objective: - I simply haven't had an initial meeting with an architect yet, that will come

What means: you name the contractor for price negotiations, but not the architect for the planning. Since effort is made when writing, it is surprising that you mention step 4 before 1, 2, and 3. One then assumes that you want to omit the architect, the most important person, out of frugality. And that quickly leads to the statement: if you want to save on the architect, the project is not for you.

I am really grateful to you for the help. Also for some structure, or rather which order makes the most sense for such a project. I do not want to exclude the architect; by next step I meant that I take your advice and first look for an architect and get advice. The goal is not to save money in the wrong place. Accordingly -> find an architect (one who has knowledge of multi-family "rental houses"). Financial framework of the family means -> how we need to position ourselves financially to handle the whole project, keyword "guarantee &Co". - but we will also consult an expert for that. It is primarily about using the property profitably and checking possibilities. Because the advantage of relying on such a property in such an area already has a high value! If someone wants to name the "best possible" sequence, that would help me a lot. Step 1 Architect has already seemed indispensable and important. My approach so far was -> find a sympathetic construction company in the area that implements extensions and fits the construction concept -> contact an architect from the company (network) and jointly plan the next steps -> plan construction financing.. I am certainly grateful for every keyword and also for rough comments :-)

One then assumes that, out of frugality, you want to skip the architect, the most important person. And then you quickly come to the statement: if you want to save on the architect, this project is not for you.

I did not mean that the OP wanted to attempt a multi-family house as a serf project. Rather: that the cost estimate should not be the trigger for whether one even looks for an architect (not as an alternative to self-planning, but for leaving it as is); because the most well-founded answer to the question of economic viability would come from the architect (if it is one who is familiar with the building type). In another thread (of the same OP), only recently pointed to such a person:

Financial framework of the family means -> how do we have to position ourselves financially to manage the whole project, keyword guarantee &Co". - But we will also consult an expert for that.

Also consider a reshuffling of the family constellation falling into the amortization period of the project due to inheritances, etc.

If someone wants to name the "best possible" sequence, that would help me a lot. Step 1 Architect has already been mentioned as indispensable and important.

There is no right and "best possible" sequence. Of course, the architect is incredibly important. But maybe just as important is that all involved family members come together and set the basic parameters. So far, it is completely unclear to me whether you own the plot or a family member, how much money (income, equity) each family member contributes, and who is going to be liable there (your keyword "guarantee"). If no agreement is in sight here, of course you don’t need an architect. A 1.6 million loan should not scare anyone off and someone among you will have to pay upfront financially, e.g. for the architect.

There is no right and "best possible" order.

For a single-family house, no, yes. It would be about self-occupancy and the paths would be as different as the people. But a multi-family house for rental is a market object.

Sure, the architect is insanely important.

You could smoke an architect in the sense of a single-family house painter, when it comes to a rental building. For that, there is a different kind of architect, they are more like CAD-affine business economists.

Perhaps just as important is that all family members involved come together and set the framework conditions.

With relatives eat and laugh, but never do business. An income property is an income property and cows belong in the meadow instead of on the ice. I didn’t want to be dependent on whether my sister married an idiot, or whether Aunt Else and Uncle Gustav quarreled over inheritance. Specialized lawyers are just as important as specialized architects – especially when the number of co-owners exceeds the number of residential units.