I like to start with "too many" coals and turn down the heat at the intake. And just open up if they are starting to run out.
But if adding coals on top of already-lit ones, I prefer lump charcoal or better-quality charcoal. I won't add unlit Kingsford blue on top; that nasty smoke it makes while lighting up is horrible. Of course, the best method is to light them separately and dump them on already hot.
For long hot cooks, or cooks where you're doing multiple dishes, I've noticed many recipes suggest adding charcoal every 45 minutes. If you manage the time you can have a small chimney going every 30 minutes and always have heat. That's not typically necessary to do in my experience, but something to consider.
