What would make my mod incompatible? I'm very afraid of this. I was making some changes to the game using events. but they would only change items created in my own mod. What is the chance of incompatibility?

A number of things could make your mod incompatible, but at that point it's just paranoia. Events are used to mitigate incompatibilities, but you usually don't have to use them unless you're doing something complex or are modifying vanilla in some fashion for a use case in your mod. As for chance, who knows? It's not a quantifiable thing if we have no idea what you're doing.