Painting wooden ceiling - Is sanding and priming necessary?

Hi dear experts. We have a house in mind that we want to buy. Of course, one thing or another still needs to be done. For example, we want to paint or lacquer the entire wooden ceiling and all walls white. It is a timber-frame house with beams and wooden panels. The wooden panels are untreated, the beams are painted dark. What do you think? Does everything need to be sanded and primed before painting/lacquering? I have seen some YouTubers who painted directly with paints that supposedly seal (block), prime, and color in one. And that with two to three coats. Is that feasible? Attached are some photos of the woods to be lacquered. Thanks for your assessments…

The wooden panels are untreated,

They are not untreated. They are treated with what was commonly used in the 70s/80s (or from the year of construction). My old childhood room also has this wood paneling.

Does everything have to be sanded and primed before painting/varnishing?

Sanding is, I think, not necessary because it is open-pored and dried out. But for . .

two to three coats.

. . You can’t avoid that. A primer is usually the diluted paint that will be used later for painting. But the wood can bleed moisture, showing through the light color. I would paint everything with chalk paint. Painting the Past or Mrs Pompadour is my tip. They also have instructions for everything. Which one is better, I no longer know – I’m not that into the topic anymore. But if you can paint a staircase with it, you can also paint such a ceiling.

But really think about it two to three or even four times whether you want to completely paint over this beautiful, truly beautiful wood in white and thus kill it in every respect... I find it a very sad trend that everything made of wood has to be painted and disguised as much as possible, as if it were plastic or metal...

Painting tongue and groove boards is not quite easy, spraying would be better, but when wood expands and contracts between summer and winter you can presumably always see the substrate. I would screw a Fermacell board on, apply textured paint on it, and degrease the beams beforehand.

In this case, I would honestly prefer to look for a house where you cannot see the roof structure...

Of course, I agree with you that this wood is really beautiful. But the house is the parental home of my partner. And she said that we already have to make quite a few changes so that she doesn't feel like she's moving back into her "old childhood room"... I can absolutely understand that, and I completely agree to paint everything white. It should look roughly like this later.

We will be laying a real wood floor, and yes—if we paint ourselves, we will try to do it with an airless device... I am currently looking for a painter in Düren and the surrounding area for a quote. I inquired with ten through the "Hammer" website with pictures and description—but received no responses. Strange. Ten out of ten window manufacturers replied. I’ll try the very old-fashioned way—by phone.