Ralph hit most of the points, but I'll add a couple:
1. Hitting the 'higher' notes is simply a matter of practice. It will feel extremely
awkward the first few times you have to use the orange key, but it will become second nature after a while. Remember that the raised notch on the yellow key is your friend. Get used to feeling for it so you know exactly where your fingers are placed. When you start getting into some of the more insane passages, you will need to make sure you are on the right keys, and that little bump is a lifesaver.
2. Definately lots of notes as opposed to long ones. Chord passages are even better, and you can really rack up the points. 8X star power on expert level 'Unsung' about made my score meter explode.
3. From what I can tell, the whammy bar does not give you more points on non-star power notes. It does boost your star power meter if you use it on starred notes (which annoys me to no end. I hate using the whammy in places I normally wouldn't just to get more star power.), but I don't think it has any effect on the score of regular notes.
4. There has been a ton of talk about a sequel, but nothing has officially been announced yet. There was an artice in GI (possibly EGM) a couple months back that the developer was talking about the list of bands they're looking at for the sequel.
Drum Hero would be awesome, but I don't think there's any way they could create a peripheral that would be cost effective. Guess I'll just stick to my real drum set and some headphones.
5. I certainly hope so. The guys at my Gamestop said they've had a hell of a time keeping it in stock, and everything I've read talks about what a huge success it has been. I can't imagine that it would be terribly expensive to develop (at least in comparison to other games), so I'm keeping my fingers crossed.
Have fun with it, and keep us updated on your progress. You'll be amazed at how easy some of the difficult songs seem once you've put in a few more hours. The learning curve is just about perfect on this game.