It's all a matter of personal preference at this point. You could just harvest it all and then you will have some different maturity levels to sample so you will be more educated on your own tastes next time. Remembering that you are learning the ropes, I don't think that you will lose that much if you do. You could leave the bottoms on to become more developed, but you aren't really forcing any nutes right now, so I don't know exactly how much difference there will be in yield. Also, for the first day or so after harvest the trichromes will keep maturing even though it's cut, so the bottoms may come out milky looking when dried even if they aren't all the way at harvest. Use your gut, no one can tell you the perfect time for your plant, you are the only one that has to be satisfied with the results.