Living in and renting out DH: Please share opinions/experiences

Hello,
I am new here, so first a brief introduction about myself/us. I am 36, married with 2 small children. So far, we have lived in various rental forms across the country. Currently, we live in a semi-detached house as first-time occupants. We are planning a move to Bavaria next year and finally want to move into our own house. Due to the "funny" market prices, new construction is currently the most likely option for us (even though we will only move in in 2023). We have gotten used to a modern standard and I am (still) not the type for a renovation. Besides, I cannot estimate the costs for this due to lack of experience and contacts.
Now I have the opportunity to purchase a plot of land. This was announced to me by phone from a FH provider. I am still an absolute novice when it comes to the individual cost structures, so for now I can only work with rough estimates.
The following conditions apply:

Plot: 900m² (possibly expandable), price approx. €460K (according to the real estate agent)
Now different options arise for me:
1. Single-family house
In prefabricated construction, according to the provider approx. €330K, I simply calculate €400K (a precise offer still has to be created)
+ risk premium of another €50K
Total investment: €910K

2. Semi-detached house
I calculate 2x €350K
+ risk €150K
Total investment: €1,300K

Now to the financial situation:
Net income: €5,000 (one income, without child benefit), my wife plans to work again after the move but we do not want to include her salary in the financing.
Equity capital: €260K (max. €300K) in more or less liquid assets. The extra €40K is actually saved for my two boys (for the world trip in 18 years :)

Our desired monthly installment is about €1,800. This excludes a lot of offers in the desired region if we want to be done before retirement. Even option 1 with the single-family house will exceed the installment.

Now to my thought experiment with the semi-detached house about which I would like to hear your opinions.
I am trying to finance the remaining €1,050K with about a €3,000 installment. The rent index in the region is €8.80/m², so for 120m² about €1,000 cold rent. Due to it being first occupancy, €1,200 would probably be realistic (but I then deduct 2 months’ rent for maintenance and vacancy, so on average €1,000 again). The building site is a 30-minute drive to Munich Airport, the next major city is 15 minutes away. The location is absolutely rural though.
With the rental income I could almost reach our actual goal of a new house in a reasonable location. The market currently does not offer this to me.
Specifications, offers, etc. will be concretized in the next few weeks. Talks with lenders went smoothly up to €800K. Next week I will inquire about the million. To be honest, with the rented semi-detached house it is not about a minimum return of x%, but rather about the possible option to move into the desired own house. That each boy would get one half would of course be a great "side effect."

Am I a genius or a complete fool?

Do you have valuable hints for me, maybe your own experiences, tips, warnings? I am very grateful for any impulses.

Regards
Matjes

Well, considering that purchase incidental costs are added to the property, the townhouse itself seems to be only a catalog price where the foundation slab and various extras as well as painting and flooring costs are incurred. Then, of course, additional construction costs arise and the outdoor area has to be landscaped, equity is partially reduced for kitchen, furniture, and miscellaneous items, and there still isn't a carport in place, your rough calculation is somewhat low and flawed. Not to mention the taxation of the rent.

With 5000 net with a family, one should still be able to sleep with a house installment.

Financial advisors always see everything positively at first.

I don't see your duplex and whether you are smart or dumb... I would rather say naive. And ignorance is no disgrace. However, one has to recognize their own threshold or rather their financial limits.

Welcome to the forum.

This was announced to me by phone by an FH provider.

The alarm bell named tied selling immediately rings in my head. So already calculate the incidental purchase costs on the full amount, not just the land.

How much is the woman expected to earn again?
I find 1 million in debt very unhealthy in relation to the income, even with rental income.

About the rental property: You have to make it not only turnkey but also ready to move in. That costs over €450,000 in total. The rent simply does not justify it. I'm sorry, but I don't see that coming.

This was announced to me by phone from an FH provider.

This is very likely a tied business transaction and you must pay the real estate transfer tax on the house and land. ONE house: House price 330000 Foundation slab 25000 Additional construction costs 50000 Floor coverings/painting in EL 20000 House upgrades according to construction service description 25000 Outdoor facilities 20000 Carport plus storage room 10000 totals: 480000€ plus kitchen and lamps For the duplex, everything times 2 (possibly 10-20000 less additional construction costs)

I am not assuming that you only want to build 100 sqm. If I now assume 160 sqm, then those are sqm prices of about €2200 - in Bavaria that is definitely not enough. Except maybe in the region of [Hof].

I interpret the keyword "Maklerin" as meaning that in this case not only does the property actually exist, but the seller is also aware of the offer or has even commissioned it - so I do not need to refer to the posts you could find here using the search term "11ant Leerverkauf." Nevertheless, I do not want to give the all-clear right away: offering too large properties to people whose creditworthiness would allow the business opportunity (and then immediately planting the idea in their heads of building wealth / retirement provision as a small-scale housing dealer) is indeed a great idea - however, in my opinion, not for the person who is supposed to play the builder. In this respect, I do strongly advocate in the question

Bin ich nun ein Genie oder eine Volldepp?

that you should cautiously consider that your business partners might at least regard you as the latter :)