1. Any soulfire must have directly impacted a being to begin affecting it. When we say it 'feverently seeks out any altered souls' we mean it does so after connecting with a being's physical structure, it doesn't home in on people.
2. The length of the coma depends on the strength of the warped creature. More powerful warped souls will take longer to be rendered comatose, and will be left in said coma for a shorter amount of time. That said, the Ascended can still continually apply Rapturous Soulfire to keep them under control. As a baseline, I'd wager ten minutes would acceptable. Curses and such are not affected by Soulfire, but may be absorbed unto the Ascended and gradually destroyed with Soul Mending. (Further elaborate what incurable afflictions you have in mind).
3. Presence of the spell will be sufficient. Life-draining the flame, casting shade magic on the flame, casting Frost Wtich magic on the flame, etc, will all extinguish it. Having a transcended dark form usually correlates with a higher strength dark creature, so they will be harder to ignite in that respect already. Ultimately the soul is still warped regardless of an altered physical form and will burn them the same as someone in a non-transformed state.
4. Ascended have always had a minor relationship with voidal magics. In our current write Silver Sect is the equivalent of the Demi-Ascended in all forms, so there isn't much of a change here besides a name.
5. That is correct for the rewrite and in the current lore. Once Soulfire connects, it feeds off of the altered soul until it is halted by dark magic, it fails to burn them away, or it burns them away.
Homunculi are no longer harmed by Ascended magic whatsoever, as they don't possess any iteration of a soul. Azdrazi fall under the same category as a regular soul, as their soul has been 'reformed' into something else entirely rather than been warped.