If you put the foil on before primer, you may wind up seeing a line of primer around the script. Especially if you use a light primer and dark paint. I had to re-paint this Caddy and applied the foil after the first color coat. I think BMF makes a gold foil? Here’s a link to a good thread on foiling script.
https://www.modelcarsmag.com/forums/topic/152097-bare-metal-foil-small-writing/