My floor plan for a 4-family house, please share your opinions

How much boundary construction do you plan? That's probably a bit too much! And around the house there should also be some hedge: no one wants a lawn where you hit the fence right in front of your nose. You need to mark out the meter there as well.

Does this also comply with the floor area ratio? I don't find a terrace facing north and the street very appealing, especially since the other tenants and their visitors walk completely around the terrace.

How much boundary construction do you plan? That's probably a bit too much! And there should also be some hedge around the house: no one wants a lawn where you hit the fence right in front of your nose. So it's important to mark that meter there.

I think the neighbors are glad that I won't be building garages with three-meter-wide roads at the boundaries, as the building authority initially suggested! So if you see sidewalks or paving as boundary construction, I have no idea what to say about that.. The garden houses will be placed directly in front of large hedges or sheds, where they won't disturb the neighborhood at all. There will also be fences and hedges, but do you want me to sketch those for you here as well?

Does it also fit with the floor area ratio? I don't really like a terrace facing north and towards the street, especially because the other tenants and their visitors walk all around the terrace.

It fits with the floor area ratio and the plot ratio etc. On the terrace sides facing the sidewalks there will be planting as a visual screen.

what if I offered the smaller ground floor apartments 150 m² of garden instead of up to 75 m²? The answer is clear, no.. That would rather be disadvantageous, because the garden maintenance expected from a small apartment would be tremendously oversized and the upper apartments would not be more attractive without garden use.

I can't shake the impression that you are under some misconceptions: 1. you seem to see your planned apartments (and yourself as a landlord?) as a gift to humanity. That is generally not true in most cases and certainly not here. Do not expect gratitude in any case, that will only be unpleasant for all involved. Renting is a business. 2. in what way is a 150-sqm garden "unreasonable" in terms of maintenance? Unless you have forgotten at least a zero or confused the unit, that is at best considered "small," if not even "tiny." Of course, it is still better than no garden. 3. The upper apartment does not necessarily benefit from a distant garden. I claim a reasonable balcony (= with enough space for some flower pots, a table with chairs, and a small sandbox) fulfils exactly the same purpose and is closer. If you want more, depending on the distance, you are better off with a community garden than with a tiny garden in which the landlord wants to impose quite a lot. Whether 18 steps and 5 meters or 18 steps and 2 km makes little difference in my eyes, the main obstacle is the apartment door. And hand on heart: would your wife endorse your "no problem, that was great" assessment?

Actually, this is about the floor plan, which can possibly be worked on with sensible ideas and tips.

Dear dobbelhaus, don’t take it the wrong way, but a lot of people here are sharing their thoughts with you. All of them are people who, as a hobby or professionally, deal with houses, floor plans, and site plans. The vast majority consider your current ideas to be underdeveloped, and it’s not just about moving a wall a few centimeters left or right. In principle, you can do whatever you want with your money – but you’re asking for advice and receiving it here – for free! When I showed up here with the first drafts for a semi-detached house project for rental, there was also a lot of criticism and many food for thought – especially the analysis of potential tenants and which tenant group I wanted to have in my house.

If I apply what I’ve learned to your house, I come to the following conclusion:
APT GF: 3 rooms with garden, single or couple don’t need the garden, may find it nice but will bother about the paths around the garden. Probably a family with 1 child would move into the apartment, who can’t afford a bigger apartment – and will move out at the second child.
APT UG/AG: 4 rooms, narrow balcony (not enough space for a lounge chair or dining table), garden to the east of the house (shade in the evenings). Families will not like the stairs to the garden, they would rather look for a terraced house of similar size. The east garden brings no benefit to a well-earning couple, since it is shady in the evening. Nothing can be placed on the nice balcony with sun, the rooms in the top floor have hardly any added value. Furthermore, the question arises whether there are such yuppies at the building site? It’s probably a small town with good connections, but more likely a place where families or average earners live – the yuppies take the maisonette penthouse in the city center.

Hence the idea to divide a semi-detached house into 3 small apartments, one per floor. Might better fit the city's demand and wouldn’t have the complicated stair solution that every maisonette concept brings – so the potential, later private half would also be better to realize.

Perhaps as a final food for thought, here we have companies that act both as developers for multi-family houses, semi-detached houses, terraced houses as well as general contractors. For a project of this size, it might be possible to bring such a company on board both as a GC and as a consultant regarding local demand. Your house will easily exceed a million, probably more like 1.5 - 2 million in total. That wouldn’t be the place where I would try to save on professional project consulting.