If I put up a plasterboard ceiling with battens to conceal the edges and screws, do I need to get a plasterer to plaster the plasterboard or can I just apply a coat of sealer on the plasterboard, a coat of primer on the battens, a coat of undercoat, followed by a couple of coats of ceiling paint?
Are you installing plasterboard (blue board) or drywall (sheetrock)?
I assume you're doing the batten so you don't have to tape the joints.
Drywall (plasterboard) has a 3" bevel on all the long edges to allow for tape & compound.
2 sheets will give you a 7" bevel that you need to cover.
To avoid this, you need to rip 3" of each edge so now your sheets are 42" vs 48" wide.