she is my best friends, who I have known for 35 years, cousin. I know her entire family already and have known her for years

I like the idea that you know her and where she comes from. Not an absolute guarantee, but much more likely that you won't have any nasty surprises.

If possible, keep this quiet until you finalize this last legal thing - exes are known to ramp it up once they realize you are happy with someone else, and your ex isn't exactly super sane.