Thank you for the explanation. I will probably use a third-party database (firebase) for payments.
Using firebase, different operations can be done on the client side, without disturbing the main server. I think this is very useful for a smoother user experience.
New MongoDB Change with Strong NodeBB Implications
Take a look, if you are deploying NodeBB with MongoDB ever, or write any code for anything that touches it, be aware that you may be forced to open source anything and everything.