Do you need to break up a large dough ball into smaller balls for optimal proving? I often make homemade pizza making the bases by hand from scratch. I'm going away with a group of friends and plan on making a very large batch of pizzas one night. I'll use a full 5kg (11 pound) bag of bakers flour.

With a pile of dough this large, would it need to be broken up into smaller balls while rising or is it fine to leave in a single large ball (I have a very large saucepan that would fit it)? I'm concerned maybe air wouldn't make it into the base of such a large mass of dough or that the weight would prevent the dough at the bottom rising. 

Commercially, how are large quantities of dough proved?
Almost every type of yeast bread dough is allowed to rise twice after kneading.  The first rise is called bulk-fermentation - after kneading, all of the dough (the bulk) gets set-aside to allow the yeast to do its job.  After this rise is complete, the dough is deflated (some people call this punching down), portioned and appropriately shaped, then allowed to rise a second time which is called proofing.

So:  first rise in bulk (bulk fermentation), second rise portioned-out (proofing).

The gas that expands the dough is carbon dioxide and it will form throughout the dough mass from yeast activity without any problem during bulk fermentation.