The body language stuff actually makes me laugh. Most of it is porn movie cliché to showcase attraction.

You see, since males are still expected to initiate courtship, when girls decide to showcase interest, their flirting attempts often fall flat on the face. It's just too weird, or too subtle, for most guys to notice.

From personal experience, besides the poor flirting, if a girl is interested on you she will:

1 - Ask stuff about your life on return when you're talking
2 - Compliment on your personality / mindset (a fairly common giveaway)
3 - Mention a quality of yours is a rare find nowadays
4 - Remember stuff about your conversations that you don't
5 - Contact you (some will, some won't)

It's important to remember atraction isn't a switch you turn on and off. Most girls that actually answer to your messages, calls etc. are actually giving a shot on knowing you better. It's up to you to make the most of it, and go for it if it's the case.

PS. Ask her out.

This is one of the problems with our society. Our men suffer from approach anxiety and are unsure of themselves, among other things. She is the one that should be asking "is he into me?" and not you. Convince yourself that she totally digs you (which it seems like she does) and ask her out, which it sounds like you were planning on doing anyway. Don't try to impress her, she can probably see that. But you have to create some sexual tension (by flirting) otherwise she might just see you as a friend. Don't make it too sexual or she might think you are just trying to get into her pants, which if that is indeed your goal then you don't deserve this advice.

No! Don't ask her if she wants to go, suggest that she come with you. You present yourself as more self-condident and in control of the situation, which is what women want. 

Otherwise you risk getting the "it doesn't matter" response, which is girl-code for "you're the guy, you decide"

You should use her for free fast food. If she is willing to give you chicken under the table then she is willing to choke your chicken.

just go for it. If she turns you down,then so what,there's like a billion other women in the world.

Maths.

well shit is that all, better lock one down soon

Yep. Ask her out; no double-guessing.

THIS IS ALLWAYS THE CORRECT AWNSER NO MATTER THE QUESTION

seriously bang her

Sorry, bro. She's just using you to make me jealous....and it's working.