Great looking R&D, hrst.

Couple of points: A plain gelatin backing probably won't work as an anti-curl layer. I think it will peel right off before processing, although it's possible it might last until that stage. You should consider applying your subbing solution to both sides. Literature suggests that erythrosine in the back subbing will work well to cut down halation. I don't see how you can incorporate a black or dark dye unless you know of one that will chemically clear during processing. It won't physically wash out in processing and will then interfere during printing. If you were coating glass, it would be a different story. Any backing applied to the plate before the emulsion coating step can be easily removed. Gelatin with burnt sienna pigment or ivory sienna black was a favored technique.

Also, I don't use a hardener in any of my negative emulsions, glass or film. Never had a problem.