Edit 20 It’s been a week since this post and a lot of people are still reaching out to me with questions which is fine. I have had a few different people reach out to me to help make YouTube videos based off this guide and more info in BFA which I’m more than willing to do. Whoever gets the videos up first I will link them here for you guys to enjoy.
My second least-favorite part: leveling ranges. Zones are divided into leveling ranges; some are for levels 10-60, others for levels 58-80, and so on. On the surface, that appears to make sense; while there are odd moments where you're presented with the content from two expansions at once, it does mean that you're more or less going through content in order, at least by expansion if not by level.
Heirlooms are special pieces of armor that level up with your character, so they have stats that are always respectable for your character’s level (up to level 110). Heirlooms that fit the head, shoulder, chest, legs, and back armor slot offer an experience bonus. The total bonus is 45 percent if you have them all. It’s also possible to acquire a ring that adds another 5 percent, but you must win a fishing contest acquire it, and that can take some time.