Mike,
Outstanding work.
I think the use of vinyl overlays would be the way to do the livery. - but you'd need multiple layers and have a lot of removing of panels/beading to do on each layer. I think a compromise of using paint - probably sprayed on for the main body colour(s), with the vinyl used to overlay beading to give the colour and lining on raised mouldings. That said, if you could match paint to vinyl colours you could do cream panels with the thin chocolate line around them as per Wenlock's recent blog posts on his 7mm bogie Brake Third.
Keep up the excellent work.
Duncan