Land Purchase, House Construction Costs 2022 / 2023 Decision Aid

For a few days now, I have been reading along diligently here. Basically, I am trying to determine whether we can or want to afford building a single-family house or if we should wait for the opportunity to buy an already existing house.
The neighbors of the apartment building where we currently rent want to split off a part of their property. We have expressed interest and are supposed to decide very quickly whether we want the land. Advantage: We know the area, we like the location, the property can only be seen from one side, namely exactly from the apartment we live in now.
Disadvantage: Relatively expensive per m², only partially developed, and it is a cul-de-sac property.

I have already looked through countless offers from rather inexpensive providers (Danwood, Town & Country, Team Massivhaus, etc.), but I still have no overview of the costs that we can really expect. Here in the forum, costs of over €3500/m² are sometimes mentioned, but it is not clear to me what is included in this sum and what is not.
It is definitely not a luxury finish that is desired, but also not the simplest standard. A ventilation system should definitely be included; we have come to appreciate this in our rental apartment (allergies). Underfloor heating throughout the house without additional radiators powered by a heat pump. These are also the two points that really make us lean towards a new build, as they can hardly or only very expensively be retrofit later in an existing building. Roller shutters throughout the house should also be part of the standard, but at least in this early phase of considerations, our special requests stop there; later on, of course, one or two more wishes will be added. The house should have around 125m², whether it will be a bungalow or something one-and-a-half stories, we are still undecided.

Is it realistic to build an inexpensive house with our special requests for around €300,000, or is that now completely impossible? Land, development, ancillary construction costs, and outdoor facilities will be added to that, of course. Northern German area, about one hour south of Hamburg. That no one really knows how costs will develop is clear, but if we are already reaching our financial limits with the financing now, we should probably refrain from buying the land, since it is no real bargain, but of course a one-time opportunity.

If you exclude all ancillary costs, land, and exterior facilities, it might still work out with the Billigheimers. But the best thing would be if you take the questionnaire on financing and fill it out. Then we will get a reasonable overview.

There would be no building obligation on the property, right? If the location is good, it might anyway be an investment consideration. You could buy the property and wait to see how the market develops? As long as the property price is not completely excessive, of course...

If you exclude all additional costs, land, outdoor facilities, it could still work with the cheap ones. But it would be best if you take the financing questionnaire and fill it out. Then we get a reasonable overview.

I will gladly fill out the questionnaire, but basically I already think I have a pretty good idea of how much monthly installment we can/want to afford over what period. Together with our existing equity, it follows that realistically €300,000 would remain for the house alone, plus all other costs. There is also money left for possible unforeseen expenses, but from the start planning €350,000 for construction costs definitely won’t work.

There would be no building obligation on the property, right? If the location is good, it might be an investment consideration anyway. You could buy the land and wait to see how the market develops? Provided the land price is not completely inflated, of course...

No building obligation, correct. The location would be good for us because we know the circumstances, but for outsiders it does have some obvious disadvantages, so I am rather skeptical about a possible increase in value. The square meter price isn’t that cheap there either. What also plays a role is that if we don’t buy the land, someone else will. Then we will first be living right next to a construction site.

I myself am from the southern NDS area… which LK is it? We are still quite inexpensive when it comes to house construction :)

How big should the house be? It should be possible.