Ive watched a few videos and they don't use primer, but their chips aren't rusty, they just build the paint layers up.
It also depends on the paint you're using, some touch up kits come ready mixed other come with primer / paint / laquer.
When I eventually get round to it, I'll post up. I don't think the finish will ever be 100%, if you want 100%, a re spray or smart repair is the way to go.
Bu the main aim is to prevent the spread of rust and hopefully a 70 - 80% finish.