I wouldn't worry myself with the lower "popcorn" buds. I'd recommend you take a small sample from the top and another from the middle range. It will give you a better overall picture. Also, in your post above you mentioned "one little leaf in the bud." If you are referring to actual, serated leaves - like sugar leaves - no, don't use those. If you are referring to a calyx (the cluster of tiny "leaves" or "petals" that make up the bud, yes! However the trichomes are unlikely to be distributed equally, do you'll definitely need more than *a* calyx! Just take a small pinch from two buds as mentioned above. Look at those through your microscope and take your time!
And while it won't be a completely accurate model, if your trichomes have mostly turned milky set your samples aside, let them dry, and give them a try! It won't be nearly as tasty or smooth without a slower drying and proper curing. Nor will it be exactly the same effect as your finished product, but it will be some indication. Besides, why just toss it? Cannabis saved is cannabis earned! (To shamefully paraphrase Ben Franklin.)
Happy growing!