Own work in new construction - what makes sense and is feasible?

[*]In some places we need slope grading or slope support. Can this be done by oneself as well?

I would be very interested in that too. Maybe someone who has done it themselves can report.

True...

First world problems. But then please don't complain about the lack of funding that was planned for expensive special requests ;)

Well, the storey increase costs €2500 including window height increase. For that, we have already given up on foiled windows (€4500) and additionally on the lift-and-slide door, which by now is really quite standard in a single-family house. I would therefore not call it luxurious but rather prioritization. That is the only extra we are indulging in besides. Above I wrote that we would spatially downsize if necessary. We don’t care about “external effect” or “representation,” but we did want a nice spatial feeling for ourselves. Furthermore, the funding was there from the start and was supposed to cushion the additional costs for the storey increase. Otherwise, we would have at least thought longer about whether we want to do it. The problem is not the fundamental restructuring of the funding, but that it hits us shortly before the building application. To accuse someone of having first world problems without knowing the background is, in my opinion, out of place.

Have you ever done such work before? I mean, more than just painting a 60 sqm apartment?

Besides the purpose, I would also consider what is feasible and affordable in terms of time and craftsmanship, without neglecting other things.

We only planned painting and flooring as DIY tasks.

However, we soon realized that we will have to outsource the flooring because we have no idea how to lay floors and the current situation does not make it any easier to constantly ask someone for help.

At first, we, as the contact persons, were in quarantine, and immediately afterwards are currently infected ourselves. And this seems to be going on throughout our entire circle of friends and acquaintances at the moment!

That amounts to 14 days that we would have missed by now.

additionally on the lift-and-slide door, which by now really are quite standard in a single-family house

No, they are not. That is somewhat upscale, but not standard.

I would therefore not call it luxurious but rather a matter of setting priorities.

When I read what is normal and planned for you, you are not situated in the reality of the "normal" home builders. Sorry.

Makes sense, for example, to buy things like a display kitchen that you like at half price and adapt the floor plan to the kitchen.
You can easily lay screed insulation yourself,
drainage of sealed surfaces,
preparation of trenches for house connections.

I would rather do all such things than the final painting work. That starts with leveling the concrete ceiling and properly finished painter's fleece, including clean acrylic joints, etc.

But in the end, it is always a matter of experience and time.
You would probably save the most time & money by self-managing the trades.