Correct Undercoat for Ceiling?

Yes Crown Basecoat Emulsion is absolutely fine to use as a basecoat or undercoat.

if a new ceiling it is worth using a primer

If it's fresh plaster then a mist coat is best, any cheap white paint mixed with water, we use approx 50/50 mix.

It will work.

Hi yes this should be fine

Primer first

Will be OK for a base coat but ideally something bit more durable for a top coat due to potential moisture rising from cooking etc

If this is a freshly plastered wall then you will firstly need to allow for the plaster to completely dry out before painting. Newly laid plaster needs to breath so you will need to apply a purposely made permeable paint for plaster or you could simply water the base coat down at a ratio of 1:1 and this can be used. Thus is what you would call a mist coat. This allows paint to almost penitrate the plaster and makes for a better adherence for the main finishing coat of paint to stick to. This will prevent any unsightly peeling over time.

You need to a mist coat first. Which is half water half paint on fresh plaster. So any paint will do.