House purchase and house construction - What can we afford

Thank you very much – these are exactly the pieces of information we are currently trying to gather together (want to), and then also to get a feel for prices & realities etc pp. Also things like "what can we reasonably do ourselves," I can get a wall painted white – if we want any kind of putty techniques – that will probably be out of the question. I can have a standard wooden floor or tiles installed, but any elaborate patterns will probably be tight. Then there are things like wanting network sockets in every (relevant) room that are then patched through in the basement – of course the question is: What does that cost more/with whom how much etc pp.

Insulation etc are naturally also topics: Can I assess that at this point in time? No – therefore the goal is to work on/read up on such topics to be able to give a somewhat qualified judgment myself and not be in the mode of "the salesperson tells me the greenest grass and I more or less have to believe it" (but ideally, in corresponding conversations then, not having too great a knowledge asymmetry).

You are still going about this the wrong way around. Currently, your plan is to gather as much information as possible and then compare the providers. This is hardly possible as a layperson; you don’t just fix the asymmetry quickly after work. On the other hand, there are people who do this every day and have been doing so for years. Not just for three weeks like you. A good representative is characterized precisely by the fact that he can sell everything not only to completely clueless customers but also to customers with cultivated half-knowledge and self-learning experts. The asymmetry is easiest to fix with an expert who is commissioned by you and only obligated to you. This expert dictates on your behalf what is to be built and the companies bid on this tender.

A good sales representative is characterized precisely by the fact that he can sell everything not only to completely clueless customers, but also to customers with well-maintained half-knowledge and self-learning experts.

then we have symmetry again. But fundamentally, you are of course completely right.

The asymmetry is easiest fixed with an expert who is commissioned by you and only obligated to you. This expert specifies on your behalf what is to be built and the companies bid on this tender

But that is only one way of building (also my preferred one), but not the prefab house option.
With prefab houses, you have the problem that after signing, only the profit and costs of the prefab house builder are optimized. There is no one "on your side" anymore.
With your budget, I would strongly recommend the architect option with tendering and construction supervision.

The problem here is that the OP only wants to choose the prefabricated house option because he has fallen for the advertising promises of the prefab builders: fast, cheap, price certainty, high quality through series production, everything from a single source,...

In truth, a prefabricated house calculated from the building permit is only slightly faster than a solid construction, it is cheap only with the low-cost provider and then only without major upgrades. Price certainty is mainly enjoyed by the provider who offers his house only from the top of the foundation slab and shifts all risks to the builder. The houses are too individual to achieve real profits through series production, and subcontracting is as common in prefab houses as it is in solid construction. Because of this mirage, the OP now wants to acquire knowledge himself and explain to the sales representatives where they are wrong. Well, that was a bit exaggerated, but that’s what it comes down to.
Having your own architect does not necessarily exclude a prefabricated house and a tender, by the way. You will probably need a few adjustments, and not every provider builds individual designs. But basically, that is possible. Or you order just the shell from a local carpentry and assign the rest yourself.

Indeed correct, but the thing with the architect is also a bit of an issue – can I judge the quality of this person? We had a pretty major renovation here in the residential complex and what the architect delivered was/is at best terrible – now it’s back and forth between expert <-> lawyer <-> architect (and I’ve learned significantly more about tenders/acceptance and construction supervision specifics than I ever wanted or hoped for – of course I can’t really engage on an equal footing, but I can follow the content). I certainly can’t explain to any representative where they are wrong (which I don’t even want to), but I can tell when someone is more or less trying to pull the wool over my eyes/talking nonsense (and I have quite a bit of experience in this, or rather I have probably often attended the same rhetoric seminars/we’ve both dealt with salespeople/vendors for years – you eventually develop a feel for serious/unserious candidates). We are not averse to the architect at all, what we are opposed to are options where we award the trades ourselves. That I imagined the FH as a significantly simpler solution, I don’t want to deny either. In the end it almost always comes down to having to find someone you can trust well enough to entrust a lot of money to (who at the same time has a more or less clear goal conflict, since he earns “his” money with your money).

Certainly, houses are individual, but the CNC machine that ultimately cuts the wall construction does not care about that; it just takes a little longer with large parts. Why should the local carpentry automatically deliver better quality than a (highly) automated production? Because the carpenter works with love for his minimum wage, unlike the soulless robot?