The idea of flushing the soil is to remove as many nutrients as possible. This forces the plant to use-up it's stored reserves. Otherwise the plant will continue uptaking and storing nutrients, which will adversely affect flavor and aroma. You'll never release (flush) all of the nutrients from the soil, but a good flush (1 or 2 gallons of properly ph'd water per gallon of pot size) has always done me fine.

If you're in "organic" (natural?) soil...every time you water you're releasing SOME nutrients from the organics themselves. In this case, I stop any additional nutrients about 2 weeks before harvest, and flush the week before harvest.

Trichomes are the ittsy-bitsy tubes with a glob of "resin" on 'em that grow from the leaf surface. It contains the THC among other stuff. If you have good eyes, you can use a 5X magnifying glass to see which stage the trichomes are at, but the pocket microscope is pretty cool to have around.

The white hairs growing out of the calyx's are pollen catching tubes that catch and transport pollen down into the calyx to form the embryo in the seed. They die-off on their own, but will also die if crushed, folded, spindled or mutilated. (or of it's calyx is pollinated)