It would seem that you are moving a little dramatically here, you met someone you like, and you have been texting with her, and you are considering the qualities you want in a wife, and want to ask her how many men she's slept with? Have you been out with her yet? A date, a kiss, a few hours together? I would start with that.
edit: I had to come back to this, you have to ask her out, before you ask her how many people she's slept with!
Get a sense of WHO she is, and you will get a sense of the answer, and then, at some point, after you have had sex, though I don't really mean directly after, but when intimacy is now longer a mystery between you two, ask her. Maybe volunteer your answer, which may be lower. If it is something you have to know, which I think is misguided, at least get some ground in the friendship/relationship first. Don't lead with some shyt like that.
LOL at 1-4 though, that's like born again/extra religious, 18 years old type of number. I wouldn't be thrown by 20. We are talking 25-35 year old women, right?