These are some great questions to think about when it comes to beginning to design our cover for Book 2. Hearing all the symbolism throughout your book, Erin, definitely gives you lots of different options on what you want to portray on your cover design - this is where you can be picky-choosy!
When it comes to choosing a cover design, I always lean towards the the Joel Friedlander approach "keep it simple". I will never forget my undergraduate Interior Design professor at URI constantly jamming in our heads the words, "keep it simple, stupid", and every design, thought, idea after that ended in a lot of erasing and re-designing to something way simpler.
Those words have definitely resonated with me to this very day. All my designs throughout undergrad AND in graduate school I have constantly repeated that quote, so it is funny that you brought it up.
I am a big fan of this passage and Joel Friedlander's views on cover designs and keeping things simple and to the point. I googled "terribly designed book covers" and came across this gem:
20 Embarrassingly Bad Book Covers
It's actually a really funny slew of books (majority I have never heard of - but all look many years old), and I can guarantee that everyone in our class could probably come up with something 10x better.
Sometimes it is harder to decide what you want to portray when you have so many options of symbolism to choose from - part of me says don't put everything on the cover, but part of me says if it all fits together, WHY NOT? It sounds like a job for lots trial and error.