(Bear in mind, I’m trying out the new editor, this is very interesting but uh, hard to get used to, haha.)
I’m very pleased to report that my first valiant attempt at a complex, seamless repeating pattern was a success! Eventually! I’m selling it on some items right now as a pattern on Redbubble and may choose to do a non-pattern version soon as well. Here’s a preview that shows the three background color options that I’m offering with it!

You can take a look at the pattern itself on my redbubble account, here!