You can use the NodeSource deb repo for the latest NodeJS for the previous 3 LTS releases of Ubuntu: https://deb.nodesource.com/setup
I would be surprised if there isn't also a PPA floating around that has Nginx with Mod Security support.
Thanks for the comment Philio! I'll check it out.
It works! Awesome and thanks for your detailed tutorial :)
I have just stumbled upon this to check if my nginx configuration was good enough. Turns out I was about 3/4 there! Thanks!