Need some help with butts on my WSM

So apparently my neighbors really liked the butt I did on Saturday. I am doing 2 on Friday for a birthday, and they asked if I can do some for them at the same time. This will be only my 3rd cook on my 22.5 WSM, so now I've got some questions. What is the normal difference in temp between the two grates? Should I switch the bottom to the top and the top to the bottom halfway through? Do I even need to use both grates? Do I need more wood chunks with that much meat? And how much is that much cold mass going to effect my temps, the stall, ect?

Thank you all for whatever help you can give me.

Fwismoker said:

You can't fit 4 butts on one rack?

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Not really sure. Looks like it might, but will be tight.

va_connoisseur said:

How large are the butts you are cooking? You should be able to fit three 8-10 pounders on one grate. As for additional fuel, it should not be an a lot (if any) additional fuel.

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They should be around 8.5-9.5lbs.

I've been using the water pan empty, just foiled over. 25 higher or lower?