Urgent - Newbie needs to be able to perform in five months, help me out!

First off, i'm just gonna state that I know that DJing and Mashing and all that is NOT easy to do. I don't think i'll be good at all by December, but I need to be able to hold a crowd by then. Lemme explain myself

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So a little while ago this group i was with was holding a party. I don't know if any of you read homestuck but this group (of over 400 members) is based around that comic, and they decided to hold a dance. The person who organized it rented out some speakers and a mixer from Long and McQuade, and then hooked it up to her laptop and set all the homestuck music on shuffle. Here's an example of homestuck music. Now, if any of you guys listened to a song or two there, you probably didn't hit the <10% of the songs that are decent at a dance, and probably hit the other >90% that kind of kill the mood. Seeing this, i jumped onto the laptop and played music from my ipod and watched the crowd. I played fast dance music when the energy was building, slow when i saw people getting romantic, fillers when people were out taking a breather, etc. Basically i was a shitty DJ, but better than leaving homestuck music on shuffle. There was speculation that there would be another dance in the winter, and I would love it if i could prevent another problem like this from occurring.

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My plan is to learn how to be a semi-decent DJ by December and use ableton live and a MIDI pad controller to create an awesome time for everyone involved. I am serious about DJing in general, and i'm hoping to learn enough to use it as a side job later on in life, but for now I just need to know enough to perform on my own. This is the MIDI pad controller i plan on getting, if i'm still serious about this in a few months.

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What i know (or think i know)

I can count beats. I can follow the Camelot wheel. I've made a shitty mashup with the worst ending ever. I've been messing around in virtualDJ but i want to switch over to Ableton Live 8. I've been doing a lot of tutorials in Ableton to figure out the program, but i'm having a problem putting things together. I've been at this for two weeks trying to find information on the internet and studying mashups on mashupbreakdown.com but I feel like it would be a lot faster if you guys just pointed me in the right direction. I've got Ableton live 8 and an Oxygen 49 MIDI keyboard my friend isn't using.

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So here's what I need. I need to know how I can move forward, what I need to learn, any good tutorials on DJing and mashups, anything i should know about ableton, basically all the info I can get. Maybe a critique on my shitty mashup if you'd be so kind :]

Finally here are a few questions that have been bumping around my head:

1: Why are there sometimes two people at the DJ stand? What does the second guy do?

2: What are some good sites for instrumentals and/or acapellas? I know about acapellas4u but that's about it

3: How do I transition to songs with different keys or tempos?

4: How do i transition songs in general

5: Is this legit at all? It seems legit

TL;DR I need to be a shitty DJ by december and hopefully get better after that, what do i need to do?

edit: In case I end up switching to turntables, what turntable would you guys recommend? My budget would be around the 200-400 dollar range