Unexpected crumbly shite existing plaster mean all the walls and ceiling need to be reinforced with mesh before new bonding and skim can be done. Extra labour, extra $$$, but hopefully buttery smooth walls will all be worth it.
I'm sure you are already but take this opportunity to move around plug sockets, lights, switches and maybe even route the odd HDMI (if you're putting a TV on the wall) as you won't have another opportunity this low effort...
...to this.
Unexpected crumbly shite existing plaster mean all the walls and ceiling need to be reinforced with mesh before new bonding and skim can be done. Extra labour, extra $$$, but hopefully buttery smooth walls will all be worth it.