I also use
Notepad++. Works pretty much out of the box, but, to do Lua you should really go through the options.
You will have to save and /reload UI in-game regardless of what you use to write Lua, IF you make changes to the .lua file while in-game. That's just the way the game is.
Lua is a Portuguese word that means moon, it's NOT an acronym in any way, shape or form.