Learning about creating useful in-editor tools

Hello. I’m a student who hopes to use GUI state machines for flipbook 2D characters.

As I did in C # Winform, I want to create a useful internal GUI that works closely with Unreal Editor.

When looking at the plugins registered in the Marketplace, it seems that this is not impossible.

But when I look at the Editor utility widget, it seems that only some simple basic UI can be added in new window independently of other editors.

I am not sure if this is the right way. It could be better when I know starting point.