A troll heals by continuously transforming into its form. Does this mean Hermione will never age, because she will always transform into a 12-year-old body? On the plus side, she wouldn't fear old age...

I don't there's a mention of trolls not aging.

I wonder if she will be able to sense all of Voldemort's horcruxes right away when she wakes up

Given that Voldemort doesn't know how many horcruxes he has, I don't think he senses all of the horcruxes.

And unless it has a limited store of energy, he will have defeated Death at that point.

Even without an unlimited store of energy it's not clear that the process is fast enough to keep 6 billion humans alive.