Here's how I start a Lang. You can pick out the parts that might work for you. I start with lump charcoal (wood is hard to come by and expensive) and a couple of small pieces of camp fire wood, which burns hot and fast. You don't want to cook with camp fire wood. Both fire box vents are fully open as is the chimney vent. The cook lid is open as is the fire box door. Once I get the draft going -- you'll see the smoke going out the chimney - I close the fire box door and the cook chamber lid. I don't start the cook until I have a good bed of coals. With both vents open, the cook chamber temp will be at it's highest.To back the cook chamber temp down, I close one of the vents and fine tune the temp with the remaining vent.
So, to answer your question, you control the cook chamber temp with your fire box vents. It's all about oxygen. My cooker is air tight and 1/4" steel -- your cooker is not and that's part of your temp control problem. You'll be leaking heat/smoke all over the place and letting oxygen in. You'll probably be "chasing" your temp through the entire cook.
If I were you I'd try a test run TODAY to see how your cooker performs. If your cook chamber temp starts to get away from you just lift the cook chamber lid for a few seconds to bring it down. I don't think high temperature will be your problem -- maintaining a steady temp will be a chore and you'll have to monitor your cooker through the entire cook.
Your smoker is going to require some getting used to but once you figure it out you'll be able to cook some good product.