One of the best brushes I've found for this is a touch-up brush I got at the auto paint store.
They are a couple of dollars for a dozen and they look like mini, one ended Q-tips.
Very good for circles & shapes, but to do the lettering and other thin-line details, you will have to use a regular brush. A very fine line type found at art supply stores.
And of course ... good luck with that!
