Woo. So many questions. I think if you follow
Chris's Midnight Brisket recipe, you are starting at a good place. You can always change your method to suit with experience.
Many people here leave water out of the pan; it acts as a heat sink/ temp stabilizer. Try foiling a large terracotta (unglazed) flower pot base and putting that in the pan.
I find that basting doesn't do all that much. You can skip it.
Fat side down protects the meat from the rising heat, in theory. I flip and rotate the brisket once in the morning.
Put the brisket on the top grate and put a large aluminum pan on the lower to catch fat drippings (makes for easier clean-up).
Opening the lid occasionally for a moment or two does no harm. Leaving it off for several minutes will raise your temperature. Adjust your temps using the bottom vents. Always keep the top vent open, or risk a sooty/creosote taste.
Good luck, stay calm. Check for tenderness in the thickest part of the flat when internal hits approx. 175 F. You'll be fine.
Don't forget to have fun.