Can I use a different primer?

[CarrotPuff]

We're painting a feature wall in the living room and are going for Farrow and Ball paint as we liked the shade most and the finish looks really good, even if it's just a sample. The wall we are painting has some unpainted plaster though, so we need a primer. My question is, is it OK to use a different brand primer, like Dulux, (as F&B is quite £££), or should we stick to the same brand? Also, do you only need one coat of primer?

Another question is, F&B calculator seems to think we need 4l of paint, but everywhere else seems to suggest we'd be ok with just over 2l. The wall in question is just over 10 square metres.

no

If you are painting over bare plaster it will be very absorbent so needs mist coating that is using a couple of diluted coats of emulsion as long as the plaster is not powdery or flaky when you should use a stabilising primer. If the plaster is sound you just use diluted emulsion either the same one you are using as a top coat or a contract matt( not vinyl). F&B eggshell paints for wood really do need the F&B primer but emulsion for walls is different

My friend is a painter/decorator and uses the same primer with all paint brands as considers it the best. So I don't think you need to match.
If you will be able to return to Farrow&Ball if necessary for the extra 2L I'd start with 2 and see how you get on.

We've had our fireplace redone so half is plastered and half isn't.

I guess we'll stick to the F&B primer then. The wall is going to be green if it matters?