Thank you so much for these flow charts! I didn't get any notifications about these posts so I just got them now.
I got my problem sorted out today! After much troubleshooting it turned out being the stroke valve on the main pump. All I did was remove it completely then inspect and reinstall. After that, everything came back to life. I am getting 1700 psi at its current adjustment but I want to drain and flush it tomorrow then I'll put the gauge back on it and adjust it the rest of the way.
I didn't find anything obvious when I removed it. I just looked it over and put it back in.
I'm still glad I went through everything else though. I learned so much!!
Thanks to all who commented! Thanks especially to Jim who gave me several very specific things to check and ultimately the suggested inspection that led to a massive smile on my face!
Great community here. Thank you all very much!