Construction financing for land and all incurred costs, OK?

One should refrain from clever sayings when one does not know a person and their previous life story which has nothing to do with this here or with the question. Thus the conclusion: What a pity about the registration here!

Smart remarks should be avoided if you don't know a person and their previous life story, which has no place here or is unrelated to the question. So the conclusion: Too bad about the registration here!

Well, the bank that is supposed to finance your property will certainly ask you this question too, and if you react like that, forget about financing with good conditions, let alone.

I wrote something about it above, now you can calculate for yourself whether you can afford it in the future. Done.

If the number is too high for you, I can also give you a lower one, but will you still be paying off the house at 80.

Why haven't you saved any equity with a net income of 4k?

Such a question is certainly justified, dear questioner! You are asking here whether a construction loan is feasible... it is basically feasible with your salary. If in the past other liabilities prevented you from saving equity, you now have enough liquidity to spare an extra thousand per month. No problem. But if it is the case that you are still paying off liabilities or, due to reckless handling of money, have not managed to save any cash in your account, then you will probably have a problem with repayment and so on. This forum is a give and take of knowledge. If others spend their time here to examine your possible financing, then you must also expect follow-up questions and not become sullen. No further advice can be given without important additional information. And you are not the one to determine this information!

With your salary, you should be able to accomplish something. However, it is important to note whether the price you mentioned stays the same or if the offer is one of those deceptive packages. How about incidental building costs, are they already included? What else is missing from the offer? Usually, only the pure construction costs are mentioned, but not the incidental building costs.
If I were in your position, I would tighten my belt now and save strictly for 2 years. With your rent, there is easily €2,000 monthly available. If not, financing will become tighter as well. As already mentioned, you should expect a monthly rate of about €1,500-2,000 if you want to finance €300,000. Then the house will belong to you after 20-25 years. Additionally, you have to calculate €300 for incidental costs for the house, which already includes reserves.
Especially if children are not an issue anyway, you have various freedoms and can also build a bit smaller. After all, you want to have it all cleaned :)

No, a construction financing is not possible based on your numbers! You will have significantly higher costs for the loan + ancillary housing costs than the current €690 in the rental apartment. Since your income is obviously just enough to cover your expenses, I don't see how you want to pay several hundred euros extra per month to finance a house???