Is the Terhorst book, which I know is a classic, worth spending $20-25 on? Am I really going to learn that much that I couldn't just learn on this board?
I say you should buy the book. It's not that you will pick up any one piece of information that you could not pick up from reading this board. A book is a different communications medium than a discussion board, in some ways superior and in some ways inferior. Information re how to retire early is taken in through a different process when taking in through the reading of a book.
One difference with reading the book is that you will learn about the Terhorst case in greater depth than you would learn about any of the cases you see described at this board. There are great benefits in gaining horizontal knowledge of a topic. But there are also benefits in gaining vertical knowledge of a topic.
Another difference is that, in organizing the material presented in his book, Terhorst had to integrate his understanding of different ideas and concepts so that his treatment of one led naturally to his treatment of another. On a discussion board, the conversation jumps from Topic A to Topic B to Topic C. You experience a collage of insights. That's fun. But there is a different sort of fun to be had in pulling the various information bits into an integrated whole, and that is better accomplished by reading a book.
I am a big fan of discussion boards. If you had to choose between participating at this board and reading the Terhorst book, and you had enough free time to be able to devote a good bit of it to reading a discussion board, I would advise you to participate at the board. But you don't have to choose. You can have the best of both worlds. I have spent lots of time on Retire Early discussion boards in recent years. But I also have read the Terhorst book three times and would probably benefit from going back to it for a fourth run-through.
This is new stuff. It is not possible for your mind to take it all in quickly. You need to go to the well, drink a bit, go away and ponder for a time, and then return to the well for a new drink. Your understanding of the material will expand after your first read of the Terhorst book in such a way that you will pick up things on the second that you just didn't see were there on the first.
You have a lot riding on getting this right. The tiny number of dollars it will cost you to obtain the Terhorst book is insignificant compared to the gain you will experience by being a little more sure that you did not make any big mistakes in development of your plan.