If it rains, you have two choices: 1) burn up some extra wood to keep chamber temps high enough to cook; 2) get it under a roof of some kind even if it's temporary like a quick-up gazebo...just inside a garage, if you have to, but probably not while a car is inside...a covered patio is the way I like to roll. Keeping it out of the rain will make temp control easier.
Were you looking for general fire control info (not sure if you're completely new to solid fuel-fired cookers or not), or specific set-points from Lang users?
Temp control is via the fire box intake draft controls and, to reduce the flow through the smoke chamber, you can reduce draft on the vent stack with the damper...don't fully close the vent or you could completely shut down the flow of heat, thus put the fire out and/or create stale/stagnant smoke which produces a bitter taste on your food.
You'll have to play with your rig to find out the best fire box and vent damper settings for the wood you're burning, ambient temps, wind and precipitation. I would start your fire with full open fire box intakes, and when temps climb over 200*, start backing off the intakes to about 1/3 or less, then watch where it goes and make further adjustment as needed to reach the desired chamber temp. Once you get a baseline, take a few notes on ambient temps and other conditions so you can find that sweet spot quicker the time time you fire it up.
I'm not familiar with any issues and can't give more than generic info for the Lang smokers...never had the pleasure of running one, but hopefully some Lang owners will jump in and offer some better baseline set-points for temp control.
Congratulations on your new Lang! I hear they are top-notch for reverse-flow smokers, and the simplicity of the design makes them virtually trouble-free.