I like where you going with it. But if this community here is thriving, I wouldn't suggest changing it because you'll lose people in the transfer.
This would work. But WordPress, unless otherwise setup, runs emails through PHPmail and that gets marked as spam. You can get an SMTP plugin like GravitySMTP and then hook it up to use Gmail's SMTP to send, just not the quickest out of the box.
The pricing of NodeBB goes from $20USD to $100USD between the first two packages. WTAF!?