SO2 at the crusher: this can range from no sulfur to 100ppm (I’ve never heard of anyone using more than that, tho I suppose you could). Most yeast are fairly sulfur tolerant, so adding some at the crusher won’t kill your native ferment possibilities. Thierry Allemand use to add no sulfur at the crusher…he lost a lot or two some years back, so it’s my understanding that he now adds 5-10ppm (a very small amt of sulfur…I use the same approach when the fruit is all clean…I use a ‘typical’ amt of sulfur in barrel after ML and prior to bottling tho). I’ve talked to Michael Dashe, a big native ferment proponent, and it’s my recollection that he uses more sulfur at the crusher and doesn’t have any problems getting a native ferment going
Killing everything but S. cerevisiae: Not possible. For one thing, Kloeckera is quite sulfur tolerant. Also, one of the benefits of native ferments is getting beneficial non-S. cerevisiae (I assume that part of your question was to understand the degree/effect of sulfur…not a desire to have an S. cerevisiae only, but thought I’d point this out anyway).
Spoilage risk: the biggest risk is the Kloeckera that will almost certainly dominate the beginning of your native ferment. Kloeckera dies at ~2-3% alc but until then it produces a fair amount of ethyl acetate. As long as you can get your ferment temp up to at least 80 degrees (75 degrees might be ok too), this isn’t a problem as EA is volatile, and the hot ferment will blow it off. But getting a small ferment up this these temps can be hard/impossible. A half ton of grapes in a T bin (double wall, so is insulated) is no problem…but a half ton in a macro bin (single wall and much shallower than a T bin) is a bit dicey. This is a real problem with fermenting 5-10 gallons as you’re thinking about. You’d have to get up to 2-3% alc without EA somehow. An exotic/creative/expensive approach is to start the ferment with encapsulated yeast…i.e. yeast encapsulated in beads in a mesh bag that you can remove at the desired point (these are intended for dessert wines, but could be used for your purpose…of course there’s no guarantee that you won’t introduce a few cultivated yeast this way). Or you could ferment a small portion of your batch with an alc intolerant cultivated yeast (putting the remainder of your batch in the fridge)…when the initial batch is done fermenting, you add it to the remainder to get it up to 3% alc (you’d have to have some way of convincing yourself that you’ve killed the cultivated yeast…alc is the easiest way…even so, there’s no guarantees you’ll get them all…but that’s always true with native ferments). An alternative is to use a Chr Hansen yeast, which have non-S. cerevisiae to simulate native ferments…I don’t know of anyone that sells these in smaller amounts tho (i.e. less than 500grams).
Another risk is the various lactobacillus bacteria (lab)…these produce VA, and a high VA can prevent yeast from fermenting. There are other factors that cause stuck ferments, but lab is the main one (high brix and insufficient nutrients being the others). Controlling lab is the main reason to use higher levels of sulfur at the crusher. The level of risk here is directly related to how clean the fruit is, and how clean everything the fruit touches is (including preventing fruit flies, which are basically a bad organism transport mechanism).
Whole cluster: wash your feet and stomp on the clusters to get some juice in there…you want the grapes/clusters entirely covered in juice, or the risk of VA producing organisms (and/or mold) growing on the surface is very high. Anyways, once you have some juice, add the sulfur and mix.
Whole berry: Not a problem with Pinot…pinot has such thin skins that 100% whole berry will still give you a lot of juice…so just add the sulfur and mix.
There. I’ve used 20 minutes productively and didn’t worry about the rain once…I’m so proud of myself!