Hello Neil,
I paint my r/c boat hulls pretty much exclusively with an airbrush and the Vallejo RC Premium Airbrush (**LINK**) range of acrylic paints, which come in 60 ml bottles. To give you some ideas of coverage, you could have a look at the painting section of my old Eilean Mór thread (https://www.modelboats.co.uk/forums/postings.asp?th=101076&p=3 – see about halfway down the page).
For the exterior of that hull (which is approximately 33" long with a 9.5" beam), I used about 120 ml (i.e. two bottles) of white primer, and (if my memory serves me) something like 40 ml of red paint and perhaps 20 ml or so of black.
In other words, these paints cover really well! 
The method is without doubt considerably slower than rattle cans, as one has to build up the paint in several thin layers, but I've not found it to be a problem.
For these large areas, I generally use a 0.6 mm needle and a 5 ml cup on my airbrush, and find that that combination works fine.
I have never tried to airbrush other paints for this sort of large surface, so don't know what sort of coverage one would get with for example Humbrol enamels.
Mattias
Edited By Banjoman on 09/02/2020 20:36:32
Edited By Banjoman on 09/02/2020 20:47:57