Is it allowed to apply paint directly on plaster or drywall?

I recommend always applying a primer. Although it requires more work, the result is much better and the paint also adheres better. In any case, on plaster.

I also prime the [Rigips] boards. For this, I use [Tiefgrund], and the paint adheres excellently on it, as does the wallpaper.

Painting alone is much better. You can save a lot of money that way. But the most important thing is that you feel like you did it yourself. The wallpaper is old-fashioned.. I think.

The wallpaper is old-fashioned.. I think.

Of course, doing the work yourself is not only enjoyable, but it also saves quite a bit of money.

Wallpaper is old-fashioned, what do you have on the walls?