Appropriate process for bulk sauteing onions?
You simply need to ensure sufficient area/a max thickness of the onion layer. You can let them simmer first in their own juices, but I have never had good results that way. You really need them spread out for sauteing. 

In practical terms for a home kitchen, this means cooking in batches. Of course, nothing stops you from using multiple burners at once, and maybe even some kind of external burner if you have one, like a paella cooker going off its own gas canister. As far as I know, there is no other way around it. 

If you don't need them sauteed but are OK with merely softened onions (no caramelization, no residual firmness), filling a pot with them and keeping them on low flame for a long time is a good option which frees your attention for other tasks. Don't forget to add sufficient fat on the bottom against burning, butter makes them especially tasty.