How to prep and paint new plaster - pva or mist coat?

I am completely new to anything like this. We are renovating our living room and had a plasterer come in and skim over 3 rough/chipped walls. They look good and smooth now, but when I asked his advice re prepping and painting them, he said that after they have dried, sand them down then use use pva mixed with water on all the walls, then after that has dried put on a couple of mist coats then emulsion.

However...

Everywhere online seems to say dont pva straight on to new plaster when its dry as it will seal it and not let the paint absorb into the plaster.

What is the correct way? I don't want cracked newly skimmed walls!

ALSO....

One of the walls was not skimmed as it was good and is just smooth old plaster - do I treat this differently? It hasn't ever been painted.

Plasterers seem obsessed with PVA I think some must put it on their cornflakes and in their sandwiches!
PVA is great UNDER plaster to aid bonding but never put it on to prime before painting!

Use a mist coat, that is a watered down coat of matt emulsion. Dilutions vary most paint makers suggest a dilution from 10 to 30% water as a rule, being British I go for the middle ground and unless there is a definite instruction on the paint use about 20% water.

On new plaster you need paint for new plaster that allows the wall to continue drying out Dulux Supermatt is a good one.

Treat the old wall the same way.