Which tasks must be completed before signing the shell construction contract?

Can you please send me a link via PM so that I can read what you mean here or what a supplier demands so early?

Which link?
Sorry, our house has been standing since 2014, we were surprised by the bill in 2013. However, the issue of connection fees for electricity (or water) was already settled before the house was built.
Every supply provider will handle this differently, but ours is certainly not an exception.
So: check with your supplier :)

So.. I just spoke with the municipal utilities.

The item you mentioned is the contribution for construction, which we partly paid when purchasing the property. The invoice you received will be the recalculation with us, since we have to pay more for 119m² of floor space due to the basement + more living space than estimated by the municipality in the purchase agreement. This will be an estimated €1700, but it should only be demanded in 2019.

That means I only have to worry about the costs of the house connections (water, sewage, electricity, and telephone) + the costs for the person from the municipal utilities who carries out the connection.

The house connections will probably be done by the shell builder, so this is more likely an item paid from the house financing.

In general, I don’t understand what problem you actually have. You have already contributed enough equity to the project (with the purchase of your property). Actually, you can then pay for everything that comes up with a loan from any normal bank (the ratio just has to be right, and it doesn't matter exactly which fund was used to pay what), so what are you waiting for or why are you hesitating like this?

I will try to explain my thought process that led me to this plan. Maybe it’s not correct that way.

The property has a value of €92k.
I need €415k for the house financing (construction costs, ancillary construction costs, and outdoor facilities). The house accounts for €355k.

There is still €26k outstanding on the property (financed variably). The outstanding amount should be paid off through our savings rate by the end of December and a mature building savings contract at the end of November, becoming free of encumbrances and included as equity in the house financing. Additionally, some items are already being settled that by the end of December will bring me to a total equity of €105k (so €92k + €13k).

That would put me at a loan-to-value ratio of just under 80%, and I would get better conditions for the house financing.
Also, from the end of December, I would have a 12-month period free of commitment fees.

These are the advantages I see. Or have I completely miscalculated?

No, definitely not. But it doesn’t matter now anyway: you will have 2000€ more or less anyway, if it’s the same for you [emoji847]

Your intention is good. Just don't give off that impression. Or rather, I wasn't really aware of it.

That would put me at a loan-to-value ratio of just under 80% and I would get better terms for the home financing.

So, on the cost side: 92K + 13K + 415 = 520K On the equity side = 92 + 13K = 105K Roughly equals = 79.8%

Has your bank ever confirmed that you get below 80%? Sometimes they have weird rules about what they count into the loan-to-value ratio.