History:
Plastering -
Plastering over artex -
Plasterboarding -
Float and set -
Rendering
Answers:
I would recommend not using paper tape but use the mesh scrim tape instead as it allows for more flexibility and not prone to splitting like paper tape. i always us fibatape as it is highly adhesive so sticks well.
A plasterer should be able to help you repair the ceiling. make sure the leak is fixed first but a plaster should be able to remove all damaged area (entire ceiling if needed) then re fix new plasterboard and plaster to a nice finish. cost really depends on size of work needing to be done.
50/50 cheap emulsion and water and give plaster a decent mist coat to seal the new plaster and give a better background for top coat of paint. as plaster is very porous if no mist coat is applied then generally it sucks the paint in so much that you need numerous coats of paint to get a nice finish.