Costs painter, plastering, floor coverings...

145x5 is not enough, at least if the ceilings also have to be done. For us, it was almost a factor of 7.5 and almost 150 kilos of paint
White fleece textured wallpaper

Since we recently faced the same question, we asked the local (Nordbaden) craftsmen.
Filling drywall, Q2 = approx. € 6-7/m² gross
Laying tiles, including adhesive and grouting, excluding tiles and baseboards = approx. € 35/m² gross

I can give you advice, try inquiring at craft businesses in the Pfalz. The prices there are often 30% lower.

You can save a lot when filling the walls because the material usage is relatively low, but the labor costs are very high. We thought for a long time about whether we should do it ourselves, but then decided against it. Filling is a job for someone who has killed mother and father.
Moreover, doing it yourself takes much longer than professionals.
I have wallpapered several times already, and with the help of my father, it works out fine. We have tiles laid by a colleague of my husband (a trained tiler). I wouldn’t dare to do that alone.

Yes, as far as the plastering work is concerned, we are still seriously considering whether we should really do it ourselves. The professionals have scheduled 2 men for about 6 days for approximately 600m² of area to be plastered.

If I were to do it myself, I would calculate about 10 days for it, and since I probably can't convince anyone to spend 10 full days plastering the place with me, I would have to do it alone out of necessity. And then I would be looking at 2-3 weeks just for this work.
By the way, it has already been noted that there are more fun things to do than plastering drywall sheets.

Therefore, it will probably come down to a compromise for us. We will have the ground floor done by professionals, and upstairs, where for example you don’t immediately need all the rooms and can take your time, we will do it ourselves.

Filling is the last job you want to do. I have seen how fast professionals were, I would have easily needed three times the time. Not to mention that I cannot walk on ladders, and working cleanly overhead also requires practice. And poorly filled and sanded surfaces pay off when wallpapering.... I speak from full experience.

If you still want to do it, and need a rolling scaffold, I have one left.