Your doing well, now take it easy when your smoking, be calm react slowly to changes. 305 deg. is not that bad of a spike. I happen to cook most of my Que @ between 295 and 350... Also every time you open the lid the temp will spike because there is an unlimited amount of air flowing into the top of the barrel and giving the coals plently of oxygen to burn hot and fast. Limit the amount of times you open it as much as possible. I know your really about to jump out of your skin to see if your doing it right, I was the exactly same way. Here's a little saying that helped me..... "if your lookin', Your not cookin' "
I would estimate about how long your going to cook or use a digital thermometer to keep from having to open to check and just leave it till its done or close to done..
Good luck with your journey down the bumpy road to fantastic BBQ!!!!!