How can I make sure I’m ready?
Before updating to 5.0, try out the Gutenberg plugin with your site to ensure it works with your existing plugins, and also to get comfortable with the new experience. Developers across the entire ecosystem are working hard to update their plugins, but your mileage and plugins may vary. And you can always use the Classic Editor to address any gaps.
As with every new thing, things might feel strange and new for a bit, but I’m confident once you start using it you’ll get comfy quickly and you won’t want to go back.
The release candidate of 5.0 is stable and fine to develop against and test.