I seem to be a little stuck. I have two problems, the first is I can't seem to "master" any of the herbs. How many times do I have to research an herb before I master it?

Second problem is that I can't seem to get the fourth piece of the gong. Do I have to complete all of the other puzzles before I can complete the gong? Also, where does the gong piece show up at once I do get the totem in the right spot? Any help would be great! Thanks!