John, your chart looks excellent, thorough and well organized. I don't think you have left out any major players...but I don't really know, because I've never considered all the traditional steps necessary to become a professional musician!
One songwriter here at MusicBanter who is trying to make it in the world as recording artist doesn't come round much, but he would probably know if you have left out any major players in your chart.
Hopefully someone else here who is knowledgeable on the subject will give you a difinitive answer to your question.
My opinion is that your chart will help the child gain a good understanding of relationships among people in the music industry.
Oh, I like how you have all those cccccooooonnnnnnssssssuuuuummmmmmeeeeeerrrrrrrrsss at the bottom of the chart. It took me a minute to realize what those were!
