Event Hacking - What am I doing wrong?

I have used ZD alot so I'm more than happy to help you but I also agree that the hex approach is the safest way.

My personal approach is to use both, which is basically required if you want to try to use ZD effectively.  Any event data you delete has to be replaced with an equal amount of data or you will eventually(if not immediately) have issues.  The editor poorly deals with moving the data so you will end up having data that the editor won't be able to read anymore otherwise.

But what if you want to delete an unused event and replace it with one half the size?  One option is to just throw in pauses(you can throw in a 0 unit pause that takes up 2 bytes of data). You can also do some fancy hex data rearranging, but that is a bit more time consuming.

I haven't even mentioned a big bug where if you edit something inside an existing event string, it can change existing event branches within that event, usually changing your CC or CB to a CA. This is the main cause of a large amount of crashes in my experience. The only way to work around this is to manually change the branches back afterwards through hex.

However...the in-program hex editor is kind of hit or miss and so I suggest using HxD or whatever you use to manually go in afterwards. Of course that begs the question, why even use ZD in the first place?  Well for me, it is just alot easier to get a clear picture of what the event is going to do because it is all translated for me right there.  If you become fluent in the event code I guess you wouldn't need that but for me it's helpful.  

I hope this helped, let me know if you have any other questions.