All good advice here.
Most chickens today are already in solution and don't need brining. If you do brine, the ratio is typically 1/2 to 1 cup of salt per gallon of water, so start in the middle at 3/4 cup and see how you like it. I also find that adding an equal amount of sugar in the brine helps to balance flavors out a lot.
Also, if you brined, do let the skin air dry in the fridge after draining off the brine. IT is impossible to get anything but a thick, rubbery skin if you do not do this. I find this works best WITHOUT rub, letting it air dry naked, and then applying rub shortly before going on the cooker.
High heat is the way to go for skin, I like running at 350. Chicken has no problem absorbing smoke, it does not require extended time at all in the smoke, so don't be afraid to cook it fast.
As for placement, if you put one over the other, then make sure not to remove the bottom one until AFTER the top one is done, regardless of temp. With brined chicken, don't worry AT ALL about dried out, overcooked chicken. You will find you can take it to much higher temps like 185...which actually produces a VERY TENDER product, almost to the "pull apart" phase. Nothing is better than tender chicken that is also juicy...so letting it go to higher temps is something I personally do regularly, but everyone has their own personal preferences and many like the meat texture at the 165 finished temp.
For vents, this was also covered. Leave the bottom vents wide open until you get within 50 degrees of your target temp and then start closing them down to dial into your target temp. It is easier to "warm up" a WSM than to cool it down, so try not to go over your target temp. Lump is easier to adjsut downwards, but even then it's best to catch the temp on the way up as opposed to trying to bring it down. Also, if you wind up at a higher temp than you wanted...don't sweat it. Just cook it. People get hung up on temps a bit to much sometimes. A steady temp is good for timing, but if you're just making dinner then running "a little high" isn't going to hurt a thing.
Have fun, and post some pics!