First off, GOOD JOB! Thats pretty awesome of you for your first night out, especially if you went solo! Seriously, good one there man!
Now for your questions..
1. For "mixed sets," approach and befriend the guys first. Ignore the girls for the most part, especially any targets. Game those guys, be their friend. Once you have conversation going a bit, ask "So how do you guys all know eachother?" Now they will freely divulge their relationships, and you wont seem obvious about it, and you can figure out which of the available girls you will target now.
2. Names are tricky for a lot of people. One thing to do, and I do this all the time even when not gaming, is to use mnemonics. Doing this often will gradually destroy your inability to remember names. Here's a good
http://www.buildyourmemory.com/faces.php .
A more fun, game-direct approach is to play the name-game and turn it around instead on them. (Props to the guy who posted it on this forum, cant remember his name sorry, LOL). When in a group and everybody is exchanging names, just give a new and different name to each girl. Make them funny if you can, but whatever goes. Usually after two or three times, the girls catch on and laugh. When they ask why you told them different names, you challenge them to see if they all can remember the names you gave each of them. They will usually do this, and when they challenge you to repeat their names back, just laugh and say, "Hey you outnumber me, I can't be expected to remember all of your names, girl number one!" They will definitely laugh (Field Tested and Approved), and hopefully you did manage to remember one of their names so you can use it immediately afterwards to show that you are just really smart and clever and funny.
3. This one is a lot harder, there is not easy answer or routine that can just be memorized. Read up on innergame first off, as well as what it takes to be an alpha male. You need to be happy, fun, and confident, and you need to project this. So appearance, body language and posture, tonality, as well as how you interact with both friends and strangers in a scene will effect this. But basically, to command or lead people, you need to project a sense of leadership strongly outwards, and you need to actually command and lead people. In RL. So be assertive, be outgoing, be strong. Yeah... easier said than done for most people.