Well, it's totally imperfect, but considering this is my first ever pseudo-realistic butterfly, I am well-pleased! Thank you Julia for all the tips you gave--it really made it easier to draw.
I used a Monarch butterfly picture from https://www.nationalgeographic.com.au/monarch-butterfly/:
I notice that the "triangle" had to be a lot wider and come to a point faster, and that helped SO MUCH with the drawing, it's amazing! When I'd finished drawing it there were so many pencil marks that I was a little overwhelmed, and didn't think I could erase and redraw well enough to make it ok to show under the paint, so I used a pen instead (which of course makes it a lot less realistic. I'll choose an easier butterfly next time! *laugh*).
Then I used watercolor to fill it in, and some watercolor pencil to deepen the orange. I used acrylic white for the spots. The concept of "cells" made it so much easier to figure out the pattern of dots so I didn't really have to count them--I knew there were two per cell (although I goofed on the lower wings, because there wasn't a double row always). Amazing how far a little knowledge goes! Here's my end result: