We've switched entirely over to Paper for everything because it works so much better than vanilla, and it also enables us to put it behind a Velocity proxy (Minecraft Java Application layer proxy also developed by the same group that develops Paper) for better scalability, more secure infrastructure, and some cool features like enabling any version of Java edition to join the same server (mad props to the ViaVersion & ViaBackwards plugin teams that make this possible!). This is impossible to do with Vanilla. We do all of our own content development creating the activities the kids do during the events, and the plugin ecosystem that someone else mentioned is hugely helpful for this. I especially want to call out how awesome the Geyser and Floodgate plugins are — they make it possible for Java and Bedrock clients to play together in the same world, which makes our customers lives so much easier.
We're hiring part time / contract developers, event hosts, and technical support personnel. If this sounds interesting, please reach out. My contact info is in my profile.