I can’t address all of your questions, but your second one, specifically – The “4GB” in your Mac refers to its RAM, not its disk storage. That’s the space you have for what you’re running at any given time, your programs, etc. Your music, if stored on your laptop, goes on the disk, which is going to be a different number – and that number is going to be a LOT bigger than 4GB.
If you are using 320Kbps MP3s, then you figure an average of 7MB per song if you play in a genre where tracks are “typical” length for most music, that being approximately 3.5 minutes. So, that means per GB of storage your disk has, you should be able to fit approximately 150 tracks. Now, you aren’t going to be able to use ALL of your disk storage for music, of course, but that should help you to get a rough estimate of how much music you can pack in.
Let me add – you should limit how many tracks you have loaded, especially in the beginning, because it is more important that you be intimately familiar with the tracks that you are playing than it is that you can play thousands of different tracks. I am also a new DJ, and currently have about a hundred tracks in my primary style, about 50 tracks each in a couple of related styles that I am trying to work into my sets, and a very small smattering of a few other styles that I have loaded just to satisfy my curiosity about mixing in genres other than those I like to work in.
Now, I may not be able to play every song that somebody might want to hear, but for most of my tracks, I know them very well – I know how they transition, I know other tracks that they sound spectacular with, and I know their idiosyncrasies – such as where they have odd phrase lengths and where I have to ride the gain during spots because it can be a little too dominant for parts of my transitions.
When I first started DJing, I made the mistake of loading my entire music collection up, and I had no idea what to do with any of it. I was completely overwhelmed. I cleared out my collection completely (not deleting the files, of course) and started adding tracks back into it a handful at a time, practicing with those until I was really comfortable with them, and then I would add in more.
This has really helped me to get a handle on my sound.
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