Thank you all for the advice! I visited two days ago, and just about managed to do everything, plus some time to revisit no-shows at the end of the day (successfully!). Sure, I didn't eat and barely sat down all day but, worth it!
I hit Islands first thing in the morning and got the boat ride all to myself. Being so early it doesn't seem like much was out and about yet, but pretty much everything there I can see at my home zoo in Edinburgh whenever anyways, so it was more about seeing the exhibits and the cool theming than the animals themselves.Those were the only major no-shows (other than the jaguars, but I saw the black one at the end of the day)!
My 'must-see' list was: Both orangutans, tuatara, sifaka (got right up close!), great hornbills, aye-aye, jaguar, Komodo dragon, reticulated python, okapi, giant otter, forest buffalo, gharial, tree kangaroo, electric blue day gecko, and bush dog. And with the exception of the last two, managed to see them all! Thank you all again for the tips!