Tell you what Dan, as a first, or even one of a few attempts at airbrushing such a scheme, that's brilliant!
Unless there are obvious finger/grease/dirt marks on the model, I wouldn't bother washing it. If there are some, just use some damp cotton wool on the immediate area, very lightly. Not sure how the spray would appear out of a double action brush, but on my single action Badger, you can hardly see the Future, until it hits the surface. Give it a quick trial blast on something first, even it's a piece of paper, so that you can see the pattern formed when it makes contact. Then, when you're ready to go 'live' make sure you keep the 'brush moving, in order to avoid any build-up or runs. If you do get any, use the EDGE of a piece of kitchen towel/tissue, to soak it up, then continue, having first checked that the 'brush is delivering OK.
If there are any gaps, bare patches or whatever, ignore them, carry on with the rest, then come back a few minutes later. The Future should be dry enough to take it; however, it is so glossy, that it will look very wet, and you'll be able to see exactly where it is, or where it's going, without problems.
Really looking forward to the next bit mate!