@vij You might want to reach out to firstname.lastname@example.org
I don't know their plugin pricing but those features don't sound like too much effort. And if you allow it to be licensed at their will (please be more precise on this, "sell them to others" might be more restrictive than you want to be) it might give you bonus points
I myself don't have much spare time right now, so I'm out of this.
If I understand you correct, you don't want to convert your database, but want NodeBB to work with users, that still will be in your existing database (MS-SQL).
It's possible, by creating your own database driver for NodeBB.
But, actually, it's not so easy. If you don't have high skill in programming, it's near to impossible.
has anyone run NodeBB using a custom SQL user database like this?
Maybe, but I never heard about it. You could try to wait for the NodeBB core developers. They, probably, know something, that may helps you.