Believe it or not, we don't get paid lol. As far as I know, the only ones making any money off this site are the owners, and they should, as simply maintaining this site is a full time job. I definitely don't get paid, I come here on my free time to bounce technical questions off of other techs and improve my knowledge and skills. The AOP section is a way for me to "give back" to the site in appreciation for all the help its given me.
As for the nitro, the welding shops in my area don't require a licence for it, it's easy to get. But as stated before, putting nitro in a system commits you to evacuating and properly charging your system back up. The tools for that alone are well over a grand, then there is the knowledge required, so proceed with caution!