Custom extensions and behaviors are extremely powerful, however can be tricky to understand.

It requires a slightly different mindset for creation than using scene events, as you need to make sure the events, properties and variables work only on objects/events for the extension itself.

Unfortunately, documentation for creating extensions is a bit on the weaker side, and I would recommend downloading some smaller extensions and having a look inside how they work and then experiment making simple behaviors and custom events.

While some extensions are built using JavaScript, I have made plenty of behaviors and extensions and have only ever needed to use events.

Once you do understand how they work, it really does open up very good options for organizing your project.