Assessment of whether house construction and loan installment are realistic or not?

Who if not you, go for it.

Solid income and top equity. We recently (early 2022) financed a proud 450k with a similar income and 100k less equity. As of today, my wife is already working full-time again and we could easily make significantly more special repayments than we are contractually allowed. Therefore, make sure you get 10% special repayments agreed upon in your home financing. Not every bank still penalizes this with an interest surcharge today. With 5%, you will be very quickly limited at the small loan amount and your relatively high income :-D

For the house calculation, however, I would roughly assume 600k, because one of these "friends and acquaintances" will quickly cancel on you or drop out for whatever reason, then you might have to buy this service completely externally. You earn so well that I would advise you to organize a family loan as a fallback option exactly for this case. With the small financing amount, you can easily pay it off from your surplus income within 2-3 years if you have to use it. You can’t just give the money back to the bank in such dimensions so easily.

Also, desires and demands usually grow with project progress, as you constantly see something new that you like or didn’t know existed in that execution, etc. You have no overview of that today. For us, it was definitely about 50k that came with the "aha effects."

Even if one of the earners goes on parental leave, a little can be compensated through a change of tax classes and parental allowance (€1,800 or €900) also comes on top, then you are still at about 5.8k or 4.9k if you use the splitting joker. With the manageable financing amount, I wouldn’t worry about your project. But really be careful and rather a bit more frugal with the self-performance topics in planning/calculation. I already regret wanting to absolutely do a "lousy drywall partition wall" in the basement myself, even though I come from a drywall contractor family and myself worked in construction for years :-D Once the child(ren) are there, you’ll think of 1000 other things :-D

Good luck!

Great equity, great salary! A lot is possible, even if leisure and clothing are missing from the living expenses. However:

Total costs new build: €500,000

Who comes up with the idea that a 180 sqm house nowadays only costs that much, so that with additional construction costs, flooring and outdoor facilities (carport/garage, terrace/driveway, garden, etc.) €50,000 comes out?
The simple calculation:
House €550,000
Additional construction costs (NDS) €50,000
Garden landscaper €50,000
Kitchen and carport €50,000
Lamps, lawnmower and mailbox can be paid from ongoing salaries.

This is quite general but often very close. You can do quite a bit yourself, but with a lucrative side job you should rather spend your time differently than building fences ;)
And acquaintances shouldn’t be counted at all. They also need to be paid. The acquaintance bonus stops anyway when a weekend has to be sacrificed. The friends bonus is probably when friends’ companies put you as an employer on the appointment list.

180 sqm calculated for 2 people is already a lot. Even if children are PLANNED. (whether they will come is never 100% certain) and when they leave after about 20 years, you are (again) sitting as 2 in your way too big house. I see it that way with my parents. The entire two upper floors completely unused, but of course still heated and cleaned ;) Just saying!! I never understand that almost everyone who builds (or has built) spends huge amounts for it and thus indebts themselves for life! (and that does not even include the follow-up financing) We built this year - big enough for the 3 of us - in a very nice "small" approx. 125 sqm house with everything you need. And only about €177k used. (see cost breakdown in one of my posts/threads) Ok, there is no carport and garden included yet. But everything else included. FULLY FURNISHED AND EQUIPPED. Of course did a lot ourselves. Especially saved a lot on the shell construction this way!! Therefore, (also currently) you have to be able to finish building the house with THAT HUGE equity alone. WITHOUT A BANK BREATHING DOWN YOUR NECK!!

Looking at your cost breakdown, I wonder if your house is furnished in a minimalist style? €1,510 for furniture? I understand you bring some things with you, etc. But it's hard for me to imagine completing a newly built house with only €1.5k.

Usually, building a house means a “living” evolution for many and often goes hand in hand with an increase in living standards and accordingly higher costs.

With your costs, however, you are probably the 0.1% exception of all home builders. Incidentally, you have to be able to do all of that (craftsmanship, time, expertise, etc.).

Respect if you actually mastered your project satisfactorily with this budget.

Great equity, great salary! A lot is possible, even if leisure time and clothing are missing from the living costs. However: Who comes up with the idea that a 180sqm house nowadays costs only so much that, with incidental construction costs, flooring, and outdoor facilities (carport/garage, terrace/driveway, garden, etc.) it comes to €50,000? The milkmaid’s calculation: House €550,000 Incidental construction costs (NDS) €50,000 Garden landscaper €50,000 Kitchen and carport €50,000 Lamps, lawnmower, and mailbox can be paid out of ongoing salaries. It’s quite general, but often very close. You can do a lot yourself, but with a lucrative side job, you should rather spend your time differently than putting up fences ;) And you shouldn’t count on acquaintances at all. They have to be paid too. The acquaintance bonus ends anyway when a weekend has to be sacrificed. The friends bonus is probably when friends’ companies put you in the appointment list as a client.

Everything can be calculated like this, but for many it’s also significantly cheaper. Not everyone has a lucrative side job, but can contribute a lot of personal effort. Many things in house construction do not require extensive training (and I don’t mean to belittle the craftsmen’s services, but some tasks are assistance and some you can learn with a bit of skill). And some also have friends and acquaintances who actually sacrifice their free time. Still common in rural areas today. Kitchen and carport can cost €50,000, but it can also be much cheaper. Likewise garden and landscaping. A lot can be done yourself and cheaper if you want (depending on the plot, stabilizing a slope is rather not possible, but on flat land you can do a lot yourself). As you say, it’s general, fitting for some, not for others. But if the OP thinks he has friends and relatives who help, then you can accept it like that.