2nd, has anyone added a 3-4 cooking grate between the stock top and bottom grates? And how much a pain to rotate said/added grates?
If you mean chunks as opposed to chips, yes, it's pretty much the preferred method around here. If you mean an all wood fire, I think that might get a little tedious feeding it given the design of the WSM.
I'm pretty sure folks have added a 3rd grate to the WSM. Not sure what you mean by rotate. It's going to be a bit more work to get to the bottom grate for sure, but not impossible.
I have done several parties for 30-40 people on my 22.5" WSM, usually once or twice a year. If you are doing ribs, chicken and sausage I would do the following: