if you've met a girl before in person and you now have her on Facebook should you number close ASAP or should you flirt with her a bit DHV or build more comfort

There's no rule, it depends if you are trying to signal intent by getting the number, or frame the n close as like a friendship move...depends on your tactic.

It really depends on the situation in which you met her and the time frame.

Assuming that you had enough interaction with her to get her Facebook I would do the following:

Comment on something she posted recently, but argue against it or say something funny.

Example:

Her: Omg, school is so hard and exams are gay blah blah blah.
You: Love exams. Hours of studying and 20 cups of coffee per day. Whats not to like? (sarcasm)

And then....gauge her response...if shes positive and responds. Shoot her a private message:

You: Hey! Whats your digits? I'm going to add it to my rolodex of semi-cool people.

Through the above process, I've always received a number.

_________________
"That shit cray"

-Hit me up with some Reps if anything I say has helped! Much love.

Thanks dude will try it and see what happens