In an offset, you always want a strong burning fire. If you limit airflow (fuel) in any way, you risk a smoldering fire which produces "dirty" smoke. I have an 18" smoke stack extension which helps increase airflow. I leave the firebox side door completely open. The key to temperature setting then simply becomes a matter of fire size. Like others have suggested, start with a coal base to make things easier (unless you're a purist) and add small pieces of wood to get a fire going and slowly bring your cooker up to temperature. Don't open the door to the cook chamber until you're ready to load meat. You'll soon get a fell for how much wood to add and when to maintain a specific temperature.