When they say 50% of the pistils, they are talking about the red hairs on the buds. You can also tell by looking at the crystal though a magnifying glass. As the plant reaches maturity for harvest. The crystals will start to become cloudy, and then turn an amber color. Depending on when you harvest will depend on what kind of high you get from the bud. If you harvest when about 30% of the crystals are clear, then you get more of a heady high. If you harvest when you have more amber crystals, then it's more like a couch high. Not sure exactly about the last part here, so look around or maybe someone will correct me if I'm wrong.
Yeah you got it, mostly. The crystals, or trichomes, are all over the buds and surrounding leaves. Clear trichomes aren't ready, cloudy or milky trichomes are full of THC for more of a head high, and amber ones are more of a stoned body high. Get a magnifier with around 30x magnification. I got a pocket microscope at radio shack for 10 bucks, it's smallest magnification is 60x so it's kinda sensitive to be hand held, but it works. Your plant is not ready yet I can tell. Those buds will beef up a lot more. The average flowering time is 8 weeks.