You want to learn control of the brush in your fingers and twirling it around to make nice rounds.... be it forward, backward, up or down. Since you don't have a teacher or instructor showing you..... a good cheap way to start is to buy some tempera paint, a 1/2" flat sable brush and get newspaper with print on it. Use the columns to pull strokes straight down. You always pull a stroke. You never push the brush away from you, unless you're in art class painting a picture.. Stay within so many lines of copy and just go across the paper making everything as uniform as possible. Make your straights vertically and horizontally. Make 100s of them. Get them so you can do it in your sleep, Next make half rounds to each side (((((((((-then-))))))))))- then turn them for tops and bottoms. Don't know how to make a half round T&B on a keyboard. You'll go through a few quarts of paint, then a few more, but it's way cheaper than buying all that 1shot and the cleanup and messes you'll make. But if you want to get the feel for the oil-based paint, pallette the paint in your brush til it feels like it will not drip outta your brush and just build it up on one side. If you make it too thin, you'll just have a mess and no coverage. Use a piece of glass for the oils. Once it dries, you can use a razor, scrap it off and start over again. If you'd like, you can put a grid on the backside to make things straight and feel easier. As far as the Mack brushes, they're good, but hopefully you got quills for lettering and not oil flats. I like Mack for the stripers and the liners and some for filling, but for lettering, I like Dick Blick's blue handled grey squirrels.
Have fun.