[Mitchelkitman]

Having painted a similar size car with brush, I can say I only used 1Ltr. painting with a brush also uses more than using a spray, as the spray puts it on thinner. I've said before (elsewhere), that I'm staggered when pros say to customers "that paint is £80 a litre, and I used 5 ltrs" or "I put on 19 coats" and other similar statements - I can only think they are making it up to inflate the price. Interestingly (on the other forum) nobody came forward to justify the huge usage!
Primer usage will give an indication on how much you need.
I should think you'll get away with 1 litre, will certainly be ok with 2 (and will have some spare for future). Make sure all paint is from the same batch.