Tony and Mac are giving you excellent advice. I would at least put a piece of foil on the lower grate, or a drip pan would work. The stone, nor water is necessary. If you have a rib rack, use that on the main grate, if you want to put some on the upper that’s fine. Anywhere between 225°-275° is fine, 250° is roughly 4 hrs, so adjust from there. Cook time won’t be affected by the number of slabs, the temp, once stabilized won’t be significantly different between grates.
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