Appropriate process for bulk sauteing onions? In doing some bulk cooking for a vacation, I needed to cook 12 sliced onions and later 6 minced onions for two different dishes; both as a first step in a sauce. In both cases, I used a large Le Creuset dutch oven. I found that the evaporation of the liquids shed from the onions couldn't keep up with the volume of liquids and I seemed to be boiling the onions rather than sauteing. 

For the sliced onions, I ended up removing half the volume, draining off the liquid, cooking the onions, and boiling down the liquid to add back to the sauce at a later step. The onions boiled / simmered for 30 mins before I took that action. The dish was fine, but was a curry, so had lots of other flavor. It was also distinctly better after I added the boiled down liquid. 

With the minced onion, the liquid eventually boiled off and I continued to cook them. It felt like it took a long time to get to that stage though. The dish was fine, but the texture of the onions was different than how I normally prepare them. 

Are there appropriate steps to take when cooking mass quantities of onions as a first step in a dish? Is it ok for them to go through the boil / simmer phase? Should they be cooked in batches? What recipe adjustments should be made?
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.