You left out the blowjob in the bathroom option.
Also, with the scenario you described, you are likely not going to end up with a number (at least not her real one) or probably one or both of you will never have any interest in seeing the other again.
According to modern pickup theory, the evening should probably go something like this:
You show up to the club with your friends. Probably buy a few rounds of drinks, talk and laugh amongst yourselves and demonstrate that you are a bunch of cool, fun, approachable guys. While you are scoping out the place trying to figure out who to talk to and who is with other people, people are scoping out you.
At some point, guys in the group typically start to go off on their own in ones and twos (depending on if they prefer to operate solo or with a wingman) to get drinks, use the bathroom, dance, explore the club and strike up conversations with people and so on.
Ok, so now you have struck up a conversation with a girl and things are going well. You should dance or talk for a bit until you have established a rapport. I avoid offering to buy drinks for two reasons. One, you don’t want to give her a creepy “I’m trying to get you drunk” vibe. And two, you are not looking to establish yourself as someone who needs to purchase affection and attention.
What you should do next, is ask her to introduce you to her friends (the ones at the club obviously). A girl’s friends will tend to get wary if a guy steals her away to hang out with a pack of dudes. You want to demonstrate to her friends that you are a swell, trustworthy guy.
Once you seem to have a good rapport with the friends, invite all her friends to meet all of your friends. Now a couple of things might happen here. Her friends and your friends might couple off. Or they might awkwardly stare at each other. Or some combination of the two. You might even get to a point where all of you are having a great time and it turns out you and a different girl in the group actually hit it off better than the girl you initially met.
Once you have locked in on the girl of interest, as a general rule, you are stuck with each other until one of you decides to leave the bar. Think about it. If you take someone’s number and continue to party, it sends a strong message that you are just collecting digits and not really that interested. Unless your friends are idiots, they will understand and should be supportive.
At some point, either your friends or her friends may decide to leave the club. This is the time to exchange numbers if you are interested in seeing each other again. If your friends are leaving, you might even want to invite her friends to come with you to the next club or late night diner or whatever. If she is leaving with her friends, don’t invite yourself along unless asked. People are generally stuck with the people who drove them there so take this into account. If she stays behind while her friends take off, that is a very good sign.