Needs to be thick enough not to tear and to "contain" enough oxygen. Typically about 1/8" (3mm) thick seems to work best, might get away with half that amount.
Even thickness is not an issue, the resin is less viscous than honey and spreads out pretty fast. Bubbles always pop in the Sylgard 184 PDMS before it cures. Takes about 48 hours to cure at room temp. ~2 hours at 195`F.
Degassing is not needed, bubbles come out even when fast cured in a hot box.
I think a new layer after every print would be a big pain (need to empty and clean the vat, recoat, etc.). I often do several prints a day back to back.
I've only tested Sylgard 184, no experience with others, but my gut says that denser versions will not absorb oxygen as readily and that's a bad thing.
Measure Twice, Cut Once.