It's a balancing act -- I honestly really want to help, but the more popular NodeBB gets, the more people need help, and that really comes at a time cost.
So we really need people like yourself -- experienced NodeBB admins who can guide others to solutions.
To lessen help/support work you really need great documentation and faq system which is searchable and brings back relevant results when searched. Then get into a habit of answering forum/support questions with answer + a link to the relevant documentation and faq resources each and every time you answer. This serves a purpose to condition users and lurking visitors into getting familiar with documentation and faq availability. Over time, end users will also help out other end users by answering the same questions with direct links to documentation and faq resources and you get end with a snowball effect
I am a firm believer in answering common questions only once so documentation/faq links will capture that answer for all to use and reference.
The hardest part is compiling that documentation and faq system entries as you go - on the fly adding to the system as new unique but commonly repeated questions pop up
Maybe make a nodeBB FAQ plugin to promote forum post/answer/replies to the FAQ plugin/display which can be edited for more appropriate format etc before final submission to an FAQ entry ?
Yes, that should not be a problem. My rather elementary understanding of the GPL suggests that it allows you to use it for whatever you want to use it for, even for a site that is behind a paywall... but the source code has to remain open-sourced.
If you have no intention of forking and selling a customised version of NodeBB, then I think you're pretty much in the clear