If you have it then Pva the solid plastered areas but no need to Pva the plasterboard.
Pva the exposed brickwork after squaring off the jagged edges.
Use a paint brush to brush on the 50:50 Pva & water.
If you skim the painted panel then how do you intend to finish off at the far right outside corner?
you will also need finish plaster, tape & skim bead for plasterboard.
mix a little bonding so its a bit stiff and dub out (fill in) all the obvious gaps and dents, & damaged areas.
skimming coats will bring everything level on one plane.
keep the bonding low to allow for skimming.
scrape out all cracks but stay off the ceiling.
sand down any previous filler.
fwiw: is the cabling modern stuff or the old black rubber sheathed stuff?