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Welcome from SC. You will enjoy this site with lots of great folks who are eager to share their ideas and tips. All you have to do is ask and keep reading. You have said that you have a horizon with a tuning plate. I assume that it is the horizon convection plate. I had one made for my offset and I love it. I don't have any experience with bricks and have not read much about them. I just know I like my convection plate. If that's not the type that you have, you will need several plates. They should be spaced with increasing openings as you get farther from the fire box.
Morning.... tuning plates adjust the heat to different places on the meat racks.... Fire brick is used for thermal mass... which evens out temp. swings...
Depending where the fire bricks are placed in the smoker, they can disrupt heat and smoke flow... not good...