Plastering the interior in a new building or applying painter's fleece directly?

And the gypsum plaster that was offered to us is something different, right?

Exactly, a gypsum plaster wall was offered, surface floated Q3 for receiving paint. Plaster thickness 12mm.

That is suitable for direct painting. In my opinion, painter's fleece is unnecessary here.

And the Kalkgips that was offered to us is something different, right?

Exactly, a Kalkgips wall was offered, surface floated Q3 for receiving paint. Plaster thickness 12mm.

Q3 can be sufficient, but it doesn't have to be. It depends on your personal feeling whether the wall is really "smooth" or not (and of course on the craftsmanship skills of the worker). We "had to" have Q3 filled again and sanded so that it was acceptable for us. But we were also quite picky.

I went through the offers last week. We have separated the commercial cleaning and painting work.

We will also have Q3 done (living room, dining room, kitchen, and hallway). Then it will be painted with matte latex paint. In the stairwell, non-woven fabric will be applied before painting, as you are more likely to catch the laundry basket, and the non-woven fabric can withstand more.

Ceilings will also be Q3 + non-woven fabric.

So, if non-woven fabric is applied, Q3 is required underneath.

Q2 is sufficient for the utility room.

Two offers would be too few for me as well. We each had 6, and they ranged from €11,000 to €25,000 just for the painting work.

... With a total of 700sqm of wall and ceiling surface

You have to plaster anyway. However, only plastering without wallpaper: one should note that plaster cannot be painted over infinitely. So if someone changes colors frequently, they should perhaps consider wallpaper/fleece.