ᐅ Home Construction in Saxony: How Can I Plan Realistically?

Hello building experts,
I want to build a KfW55EE bungalow with 100m2 (approximately 1,076 sq ft) turnkey with Heinz von Heiden in Saxony.
The plot is provided by my parents, 1800m2 (about 30x60m / 98x197 ft), relatively flat.
A sewage connection was laid and paid for years ago. A few small shrubs and trees need to be removed.
I am 52 and my wife is 47 years old, so we don’t have much time left to pay off a loan.
I currently earn €3000 and my wife €1500. We still live in Bavaria at the moment and will have to change jobs anyway because we need to move. We currently rent and pay €1250 including utilities for 115m2 (about 1,238 sq ft).
We have around €100,000 in savings, but we only want to use about €45,000 as equity in the financing to keep sufficient reserves for the upcoming move and any unforeseen expenses.
The turnkey bungalow, including groundwork and soil survey, should cost €178,000. We plan to do some work ourselves, such as painting walls and installing the flooring. We also plan to build a prefabricated garage, 6x4m (about 20x13 ft), for one car, bicycles, and garden furniture storage (around €10,000).
What additional building-related costs should we plan for, and which of these costs should be included in the financing?
We would be very grateful for any advice.