Generally the ECB runs a bit different temp between the upper and lower racks, but not enough to cause you a problem. You will be in and out doing the 2-2-1 thing, wrapping in foil, unwrapping to finish, etc. If you want to swap levels do it then.
Every time you lift the lid on your ECB you lengthen cooking time. You loose the heat and it has to come back to temp. I have heard some say you lengthen cooking time an hour each time you lift it, I can't say that has been my experience, but it takes a bit to come back. Plan ahead and work as fast as you can. You will do fine.
ENJOY!
