Thistle bonding should be 8mm, so 10mm would be acceptable but you may find doing 5mm first wait it to stiffen up then another 5mm, otherwise you may be wearing more than there is on the ceiling.
I attempted 1 wall of plastering myself & I've seen a lot of plastering being done. I foned my mate before I had even done a square metre to help me!! I Tile, My mates Plaster!! I will stick with that.
haha I knw plastering is an art in itself mate my cousin can do near enough anything.... accept plaster so that says something but I just need it as flush as I can then the plan is to sand it and paint job done lol