Gillian, you have learned a lot. Congrats on seeing ghostwriting for what it is. In the beginning I wrote for bylines, which did open doors for me later. In my career as a writer I have written lots without a byline but got a paycheck, and have done plenty of moonlight work with and without bylines.
I consider every job a learning experience. And once I was writing for money it was important to have a firm understanding of my value so I could price myself properly.
One also learns — the more experiences you have — a couple other things. (1) What you do and don’t like writing about, and (2) the kinds of clients you do and don’t like writing for.
Your whole career is ahead of you… Sounds like your head is on straight and you’ve learned a lot. Most of my career is behind me and the one thing I especially learned was… It is totally amazing in retrospect how much you can produce in a lifetime. At this point in time you really can’t imagine where it will take you.