Welcome Wakka
Well,
for API look at the WIKI of this site. For advanced information you can look to the "source documentation"
here.
Look at the
Developer Ultilities:
Recommended add-ons: zgoo, click4info, TextureIt, DevTools.
For NotePad++ look at
NotePad++ ESO AutoComplete.
Especially, if your are native English speaker and/or use english client, beware of localization. It is a well-known trap, that returned strings of other languages have "garbage" at the end:
http://www.esoui.com/forums/showpost...21&postcount=8
You can switch language in-game:
Khrill Language Selector
And once you did your first add-on I recommend to read this:
http://www.lua.org/gems/sample.pdf