Bank does not accept own contribution

Understood. That means there is a bit of risk involved. But how is an inspector supposed to check the solder joints or how the cables were laid at the end of the construction? They won't be visible anymore.

Acceptance/inspection according to construction progress, certainly? So multiple times, just like it would be with a general contractor in house construction.

I believe you are underestimating the possible sources of error. Today, construction is not done like it was 30-40 years ago. Back then, it didn’t matter if the window was properly sealed. Just put in some PU foam and done (Nothing against PU foam). Somehow, there was always a certain amount of draft. Today, everything is airtight. If you make a mistake, you end up with mold in the corner. Stones are no longer laid with mortar today but glued. And, and, and... It may not be rocket science, but it is the interaction of so many trades with different technical requirements. Don’t get me wrong, anyone with time, energy, and enthusiasm can do a lot with EL. Especially if they are perhaps a craftsman in construction themselves and know other trades and work closely with them. But that’s not you. And I don’t buy that you can acquire this expertise properly on your own. The architect supervises... but he doesn’t put himself through it to that extent. And certainly not if he isn’t paid 50k for construction management. Why should he? He doesn’t even know which job to take on first, and then he should also be responsible for yours? There are so, so many points in this that just sound unrealistic. I see this as a project doomed to fail, but I am happy to be convinced otherwise... so far you haven’t at all.

I think you are underestimating the possible sources of errors. Today, construction is not done like it was 30-40 years ago. Back then, it didn’t matter if the window was properly sealed. Just foam it with PU foam and done (Nothing against PU foam ). Somehow, it still leaked to some extent. Today everything is sealed. If you make a mistake, you get a mold corner. Stones are no longer built with mortar today but glued. And, and and... It may not be rocket science, but it’s the interaction of so many trades with different technical requirements. Don’t get me wrong, if you have time, energy, and enthusiasm, you can do a lot with EL. Especially if you maybe yourself are a craftsman on the construction site and know other trades and work a lot with them. But that’s not you. And I don’t buy that you can acquire that knowledge professionally on your own. The architect supervises… but he doesn’t do it to that extent. And certainly not if he’s not paid 50k for the construction management. Why should he? I don’t even know which order he should accept first and then he should also stand in for yours? There are so, so many points in there that just sound utopian. I see this as a project doomed to fail, but I’m happy to be proven wrong… so far you’re not doing that at all.

Here’s someone who did it themselves too. Construction method is pretty much identical except for flat roof (I need a pitched roof): [MEDIA=youtube]HFxtcQcbMjo[/MEDIA]

An architect can't check every little detail like properly soldered copper pipe connections.
He is not an HVAC specialist when it comes to installation.
A small leaking solder joint in the underfloor heating is enough, and you almost have a total loss.

Well, hardly any soldering is done anymore. Press fittings are installed and then pressure tested for over 48 hours.
Although underfloor heating is usually MSVR anyway, and there are no joints in the floor.
But that doesn't change the plan itself.

Own experience: a friend built everything with individual contracts involving a lot of electricians and friends. But there were bricklayers, roofers, electricians in the family or among friends.
All in all, it took a good 2 years, and the old-school master bricklayer provided a LOT of consulting support. I sometimes really cursed as a helper because aids like cranes, pallet trucks, etc. were saved on. Only because we have really been friends since childhood did I still help out.
What I want to say: despite professional support, it all took 2 years. That was anything but a gift.
I do think you have made, or are currently making, a real plan. BUT: First find an electrician who will sign for relatively little money. Or a window manufacturer who will come for one element. Or, or, or. Some things are rightly subject to mandatory professional services.
I also consider such a planned project rather difficult. But I am also happy to be proven wrong, as I absolutely support self-reliance.

Acceptance/inspection according to construction progress, for sure? So, several times, just like it would be with a general contractor in house construction.

That reduces the risk somewhat. If after the first construction phase I notice the inspector complains too much/repairs would be too expensive, I can consider hiring specialist companies for the rest, at least for the critical parts.

What do you think of a self-build or shell construction house in timber frame construction where you always have a site manager from the construction company who provides assistance and conducts inspections ... ?