What do you think of the payment plan? Opinions and experiences?

"insignificant remaining services" is also a trap. Significant is only what would prevent you from moving in, such as a missing window. A defective window, on the other hand, is only insignificant, since you can still live inside. Electrical wiring that only partially works is also insignificant, since you can still live inside. etc. So you always have to pay and then chase after the defect correction.

Experience: Company still gets money: the craftsman is at the construction site the next morning and fixes the defect. Company already has all the money: you get an appointment at the earliest in 4 weeks after long begging and threats with a lawyer.

Well, what does trap mean. It’s not that clear. On the other hand, you can understand the BU. If an outlet is crooked, I simply must not withhold payment to the electrical contractor. That is fair.
Are there really BUs that have this clause removed?

In the Construction Code it is actually clearly regulated: "If the costs of remedying a defect amount to at least 10% of the agreed remuneration, then a non-insignificant defect pursuant to § 640 para. 1 sentence 2 of the Construction Code is present, so that the client is entitled to refuse acceptance of the work. If the defect remedy costs amount to at least 10% of the agreed remuneration, this constitutes a not insignificant breach of duty by the contractor, so that the client's withdrawal from the contract is not excluded pursuant to § 323 para. 5 sentence 2 of the Construction Code."

If a socket is crooked, I am simply not allowed to withhold payment to the electrical trade.

No, but proportionally. Crooked socket = €10 retention.

Well, the screed is usually done last with "turnkey". So I think it's okay. I would prefer the final payment to be higher.

That's not okay at all. With just the screed, everything else is still missing. No heating, no electrical work except for a few cables, no exterior plaster, no painting, no floors, no doors, no front door... nothing!

You can easily add another 150,000 euros, and you would have paid everything except for 3%. You realize that yourself, right? Not good!

Flooring and painting are usually not included in the scope of services of a general contractor for "turnkey" projects. But yes, the fine installation of electrical systems, sanitary fixtures, possibly heat pumps, etc., only comes afterward. 97% at this stage is a joke. I would estimate 75% as appropriate. But as I said, in my opinion, the overpayment occurs already at the shell construction stage, so much earlier. My shell construction costs about 20% of the construction volume, just for comparison. Earthworks 2-3% and fees for engineers about 3-4% at this point.

Yes, an overpayment occurs here earlier. But a shell construction without a roof can already account for 40% of the total costs, that was the case for us and is not unusual (with basement and garage for us [170,000]).

Sure, depending on the object. Those who build monolithically will also have a larger share of the shell construction.