Custom extensions can definitely make a huge range of tasks much easier. I have never done exactly what you describe, but I can recommend using object parameters more. They make it much easier and more convenient to configure objects and work with them in general:
For example, for creating NPCs and configuring them, switching modes, setting everything up, making variations using the same setup. Checkboxes, default values, separate fields with parameters and strings, the ability to select strings or numbers from lists, load external resources, set colors, and so on:
This helps to keep the project more organized and allows you to check/change their values more conveniently than with regular variables.
For example It would be very convenient to use such actions/conditions in conjunction with an item_list structure variable containing damage stats, names, price etc, and you could still refer to all of it simply by a drop-down list:
You can use them both in scene and in custom extension events.
I’m not sure if this will be useful to you, but in my opinion, using custom extensions and behaviors without this doesn’t offer much advantage over regular scene events or external events with variables.