Welcome to The Obsession!
Best way to learn temp control. Fill up the basket with coals, Light a small spot, Open the top vent 1/4 turn and bottom vent just barely open (pinkie). Sit back with a cooler of your favorite adult beverage and watch the temp. Once stabalized, make a note of it, bump the top vent another 1/4 turn and have another beverage. Again, once stabalized, take notes, bump the top vent again and maybe open the bottom a bit more. Keep doing this until the dome reaches maybe 450F, as almost all your cooks will be below that temperature (except the burn-in and doing pizzas). The vent position/temperature correlation is very repeatable, assuming you have enough charcoal in the basket.
Secondly, DON"T CHASE THE TEMPERATURE! If the KK is heat soaked, you're not going to be able to lower the temperature easily if you overshoot your target. Also, it's BBQ, not rocket science. Plus/Minus 50F off your target is nothing. Just roll with it. You won't notice any difference in the results, only the cooking time might be slightly affected.
Good Luck, Post Pictures of that all-important virgin cook!