flushing has whole threads devoted to what a load of horseshit it is, look them up, not going to rehash whole threads worth of shit for you.
as far as light spectrum goes, traditionally, something close to 6500 k is used for veg, but since leds have become a lot more popular, its become obvious that they veg very well under 3000k to 7000k, with little real difference. if you have a particularly stretchy strain, they will benefit from a lower k value light. that's the only real reason to give a shit about k value in veg.