If you put too much shit in, the microbes dont work as well, they have to compete with every other airborne microbe that lands on the fresh material. When you add a little at a time, the 'good' microbes can just take off. (Similar to mush cult).
Never heard of Espom Salt supplementation (MgSO4). Dolomite lime (CaMg) is a normal supplement though, as it helps keep the pH from falling too low.
that's not really how it works. If you have lots of worm and things don't get compacted you can add lots at a time. Too much food uses too much oxygen, which leads to anaerobic, sour conditions the worms don't like.
The reason for calcium supplementation is worm biology. They have a calciferous gland that injects calcium carbonate into their food on the way in. That part is crucial to their digestive process. Keep your bin aerobic and the pH will stay right assuming you don't go crazy with acidic stuff.
As for microbes from the air, you want them. 99% of them are good.