From what I've read, it was a lot faster to clear the quest log at 60 and just head to Hellfire then it was to run around E.PL/W.PL/Winterspring etc turning quests in at 60.

I'm not sure if this is still true or not for WotLK, but in BC you were better off without any quest log clutter then you were to turn in a bunch of already completed quests.
I suppose if you log off in SMV at a quest hub with six quests to turn in, and are bound in SW which is a harbor for one of the new zones... that won't hurt your cause much.

Basically for preparations...

Have every toon you'd like to level to 80, as close to 70 as possible.
Clear as much as possible from their bags.
Have a few stacks of the best food/water/bandages available.
Possibly some elixir's but space is probably worth more then a lot of these.
For maximum profit, gathering skills at 375 and sell everything you gather while leveling.
For maximum leveling, ignore gathering while leveling.
Be camped the day before the expansion where the expansion boat/zepellin arrives, so you can get started as soon as the game is live.
Catch up on your sleep before the expansion, you'll probably be short on sleep for the first little while.