Atlas,
Excellent questions.
First of all, there is a difference between an abundance mentality, and absolute abundance.
An abundance mentality doesn't mean you have to have a physical abundance of women, nor does it mean you
have to be sleeping with and dating multiple women to have it. Sleeping with and seeing multiple women is just by far the easiest way to get it.
An abundance mentality just means that you recognize and believe that beautiful women exist everywhere, and as such, you don't have to get caught up with one, and you don't have to take shit from girls who are incompatible with you, because so many girls exist! =P
Absolute abundance is the next level though, it's the acceptance, recognition, and belief that the most gorgeous women in the world aren't that hard to find either; basically 10s (on the 1-10 scale) also exist in huge numbers so there's no reason to take shit from a 10, or settle for a 10 who is incompatible with you.
In high school, having a physical abundance is best (I graduated last year and was a pussy with women until the last half of my senior year), but you can still get a mental abundance by telling yourself that what I said above: that "beautiful women exist everywhere... and so on and so forth" <-- Tell yourself that every day and the mindset becomes habitual and you naturally embrace that idea over the period of about 30 days.
With closing, I'm not sure what you're exactly asking, because closing with a woman can mean closing sexually, number closing, closing a date... and each of those come with a different set of factors... so if you'd care to elaborate a bit, I'd be happy to help
Cheers,
-Richard