plasterboard over artex ceiling

Hi all

I have artex ceiling all over the house . Artex itself is no bad it has small spikes.I hired somebody to put the plasterboard over it and the skim the ceiling.
I have no idea of what to look for whether he is doing a good job or not..

Can you pls advise

1. Does he need to take off the spikes of artex before putting the plaster board.
2. Does it need sealing, i mean where two plaster board join and end of wall.
3. Does it need to be sealed with PVS/primer before the skim.
4. How may coats of skim, what kind of plaster need to be used?
5. Any thing else i should look that the job is done properly.

thank you very much for your reply

 

thanks guys