If your still struggling/unsure? Get a local rep out from Weber or Parex or Fassa who can advise a complete system so your covered rather than a bit if this followed by bit of that etc. Any competent renderer should know how to sort your job out to be fair. Try googling some local ones and check...
It's s**t mate use Bondit green exterior grit it's waterproof and you can put loads on with it all pulling in at the same time. The yellow stuff is as bad as blue grit. Waste of time mate don't waste your money
Thought it was 2 ceilings? Even so, that old topic of you won't get away with charging this and that regard where we are based etc. I myself think if I won't get out of a job the money I want? I leave it simple as that
Can use an old piece of mortar to rub up and down the damaged edge. But as sand cement is rare as hens teeth on site these days use the oil stone method as mentioned above. Might be an idea to dry bum whoever responsible for the boarding while your at it too??