Welcome to the little club.

My advice? Start slow, and small. Play at least one class you know - with RAF you can level many characters, so if one doesn't work out, it's no big deal. If you 3 box, go for the holy trinity of tank/healer/dps, you should be fine. I went all the way through Northrend to Icecrown with 3, there were maybe 3 or 4 encounters that were truly hard, and I had no dedicated tank or healer.

If you're going to level toons from level 1, you have plenty of time to see how your macros will work, and what strats to use - it's jumping in at high levels where it can get confusing fast.

Also, if you don't have one, get a guild and a bank. It will help a LOT. I spent a lot of my money leveling on bank slots instead of epic flyers, and I don't regret it at all. I have 5 bank slots, and I have a LOT stored away.

As for the rest - keep reading here. All you need is right here, and if you truly get stuck, ask.

And most important - have fun!