My kitchen was plastered 3 months ago. Can I use just contract paint or do I need to use contract and another paint on top?

Use the contract paint as a mist coat 50% paint and %50 water do not use a vinal paint as the plaster is still newish and you need it to breath. Dulux suprmatt will do the trick and if you want to do for a stronger finish then a kitchen/bathroom paint is what you want.

you can now use vinyl based emulsion but just make a thin mist coat and then two full coats

you can use contract paint but it doesnt have a very durable finish, i would use it to mis-coat the walls then finish in vinyl matt or mid sheen.

Contract matt emulsion is fine for top coat but the only thing is its not wipeable.

use contract paint to seal the walls and ceiling but water it down first let it dry . Never use emulsion in kitchens and bathrooms because of steam always use eggshell or kitchen and bathroom paints .