I went through the same process as you a few months ago and I was able to find much of what I needed between these sources:
The docs: https://docs.nodebb.org/en/latest/
(google searches will often send you to out of date versions, watch the urls!)
The source: https://github.com/NodeBB/NodeBB
(Having a good IDE helps with making sense of the source and doing good searches)
I got a lot of help from purchasing Webstorm IDE (https://www.jetbrains.com/webstorm/
) I've also heard people here like using Sublime Text with a lot of plugins installed.
Finding any existing plugin with related functionality to what I was trying to do was very helpful. For some reason, I found the Mandrill email plugin really helpful at first (https://github.com/akhoury/nodebb-plugin-emailer-mandrill
), but just dig around until you find something with functionality related to what you are trying to do.
Lastly, I'd search and ask questions here under the plugins category (https://community.nodebb.org/category/7/nodebb-plugins
). I've asked a lot of newb questions and the community has been awesome.
Also, after developing a few plugins myself, I wrote this Slush based tool for generating NodeBB plugins based on a number of questions: