How to prepare painted ceiling skimming?

[JP_]

Will want the whole room skimmed for smooth finish.
Will all the paint need to be scraped off first?
Or would it be best to just get the new bit of ceiling (chimney was removed) plastered and paint the whole lot (white, not brown - why did the previous owner have brown ceilings!)

 

[bobasd]

thers maybe asbestos in the aertex swirls?
you could fill the gaps an tape the repair piece - nock off any high bts.
pva twice an use a coat of bonding then skim.