3. There's a Semi-Unspoken FastPass Tier System
One fact that surprises many WDW guests is the existence of FastPass+ tiers for attractions at each of the four parks. At Epcot, the "Tier 1" or "Tier A" (aka most popular) attractions are Test Track, Soarin' Around the World, Frozen Ever After, and the "IllumiNations: Reflections of Earth" nighttime spectacular.
What this means is that you can only have a FastPass for one of these attractions at a time, while you can have multiple simultaneous FastPasses for everything else in the park, i.e. "Tier 2/B" attractions. However, if you use all three of your allotted FastPasses on a given day, you may make a fourth selection for any available attraction, whether or not it's in the first or second tier.
Disney World doesn't really advertise the existence of these tiers, and most people only discover them by attempting to schedule FastPasses on their account, only to be disappointed they can't do Test Track and Frozen Ever After back-to-back. Thankfully you're reading this article and can go in prepared ;)