I apply my spices by pulling up the skin and pushing the spices beneath the skin. I find the spices permeates the breast meat better using this method.
I follow Thermoworks suggested cooking temps for chicken and turkeys. Pull the chicken/turkey when the breast meat reaches 157 degrees. Loosely tent the bird with foil and let it rest for at least 30 minutes. The temp will continue to rise to 165 + and the juices will redistribute throughout the bird. If you carv the bird sooner it will loose a lot of it's juices in turn drying out the breast meat. A chicken should only take roughly between 1 hour to 1 hour and 15 minutes. Cook time will vary depending on your ambient temperature and wind conditions. I usually start checking the breast meat at 1 hour. If you allow the breast meat to reach 170 while on the rotisserie, you will end up with dry breast meat.
One trick I use is to place the charcoal baskets in an offset position as in the photos below. I also spit the bird with the legs and thighs towards the charcoal baskets. The dark meat can tolerate the higher heat with it needing to reach the suggested 175-180 degree range. I do not put any water in the drip pan below the bird.
This is a photo of my 1980's Weber kettle owners manual. It has the recommended amounts of briquettes per Weber to be used on each side when cooking indirect. It has a break down for SJ, 18", 22" and 26". The 22" is highlighted as it was the only size I owned back then.
I have always just followed this guide and start with 50 briquettes (25 per side) when cooking indirect or using the rotisserie. I then add 8-9 briquettes per hour to each side. I run my lid and bowl vents wide open when using the rotisserie. There is so much air gap when using a rotisserie, I don't believe adjusting the vents make much difference. My lid therm usually runs at 350-375 degrees.