Re-plastering interior walls

Hello everyone

I have just registered

A few months ago I bought a small old finca (about 40 years) in the tropics
Since the walls are not straight, and I had to lay the electrical installation flush in the wall, I want to plaster the walls anew and straighten them at the same time.
When I place a straightedge vertically against the walls, I notice deviations of up to 1.5 cm, so it is a slightly bumpy situation.
In the past, no one cared about that but I want it done properly.
There are no real experts here in this third world area (it is in the countryside) who can give qualified advice anyway, but with plaster profiles the few available can achieve a straight plaster.

Now to my actual question.
The walls are painted (directly on plaster) and the old paint seems quite firmly attached to the wall
Which primer should I use so that the plaster adheres?
And how thin can I plaster? That is, how many mm of plaster at least.

For your information.
The annual temperatures here are always between 27 and 33 degrees, only at night sometimes 22 degrees.
And the humidity is 60 to 80% throughout the year. Typical tropics! Gypsum could therefore be tricky.

Thanks and regards,

The resettler!

Here, the necessary information would be on the product itself
Reduce the color or prime strongly for consolidation. Plaster from 1cm.

Thank you
They probably like this here too, but my Spanish is lousy .... and I don't always have my glasses with me.
What are the usual hardware stores for DIYers in Germany do exist here too, but unfortunately without the more extensive building materials trade
and rarely with trained advisors.
Let's meet one ... let's write down the name and place.

Very good priming also seems important to me.

One more question, should I use a different type of plaster for smaller dents that are over a meter long, which I can apply thinner?