I don't use bentonite, so I can't say. You can add it before bottling, if you want to use it for a clarifier, but it's almost never used in most wines.
But no on the campden and yeast.
You mix up the must, with the campden tablets. Add pectic enzyme 12 hours later, and then 12 hours later add the yeast. Just like the directions say.
I use bentonite in all my wines, my only explanation is because that's the way I was shown. I mix it in before I add my yeast, although you can also use it before bottling.
Ideally you want perhaps 12 hours between the addition of each: k-meta, pectic enzyme and yeast. Simply has to do with the gas created by the k-meta and enzyme since it can interfere with yeast taking hold. BUT many people add them all at the same time and wine does fine. A choice you make. Personally I wait at least 12 hours between.
Bentonite is used before or after fermentation....again a decision you make. I prefer to add it preferment because it helps control turbulent, violent ferments and the wine seems to clear and degas sooner.