Depending on your budget I highly recommend pure crop 1 it's actually for hemp. But I saw how many people say no to neem oil in flower, here is how I use it and do not get the neem taste. So spray your soil, stems and buds. Let it sit for like 3-4 minutes do not let it dry on buds your going to gently spray the buds off with water. Basically rinse the neem off the buds. You might lose some trichs but it's better than it tasting like bitter sour pickle earwax. Leave it on the stems and in the soil it will keep the thrips away. Use neem oil all through veg and be sure to spray the top of the soil. It's a preventative bug spray not a insecticide.
As for your first question. No I'd wait at least 2-3 weeks and let them babys swell and trichs get right. You want at least 10% amber, I've found that if you wait for 10% that will give around 87% milky and 3% clear. But definitely start flushing beforehand. Catch a fade in those leaves