Air intakes are a good thing, but, a lot of Santa Maria pits do not have them. All of the built in pits I have designed have them as part of both the clean out system and the ventilation system. But, they are not needed at all. A fire grate only needs to be a couple of inches off the bottom of the box, no more. But, as Dave mentioned above, you do not need it, I think it makes it easier to get the fire going.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"I'm Armenian...perhaps...but then again...maybe not..."