In the meantime, while you wait for someone who can give you a better answer,
What you said is true: more hands = more accurate. I think you can say they are accurate when they don't change anymore? But this would mean you are not changing your game in time ... so unless you play the same way for a looot of hands, you will never be able to say these stats are accurate, because they are changing because of variance and you change your playing, play other limits...
But ... for certain stats you don't need a big sample at all for them to be close enough. You should think of it like this: The more often the situation occurs, the sooner the stat will be 'accurate'. So preflop stats like you mentioned specifically: VPIP and RFI or PFR take less hands then something like 5bet-range or whatever.
I guestimate you need a few thousand hands for your VPIP/PFR to be very close, but could be sooner. But this is really a guess. At least you don't need 10K hands for VPIP/PFR. A lot of times my hud gives my averages after a few 100 hands already.
Your winrate would need a lot more hands, if I had to guestimate maybe a few 100K hands but this could be more. Other people might have more experience and give you a better answer to this.