This recipe works for any small, oily fish and I've used it a lot with mackerel, herring and small bluefish. The reason you have a double brine is that the first one clears out the slime and blood from the fish, and the second one seasons and flavors it. Don't alter the first brine, but you can alter the second as you see fit.
Wood choice is also up to you. For fish, I prefer fruit woods such as apple, or alder, maple or oak.