Josh, what kind of development are you planning? Its kind of difficult to point you in the right direction if we don't know what you're trying to do. You must already have some idea of what you want to build on the phone. I think learning python is a great start for working with the N900 in general as its pretty "native". If you plan on making any games, SDL is a good library to look at for quickly getting "good" graphics on the screen with minimal code. SDL + C++ would be my suggestion, iirc there are also SDL extensions for python, but your mileage may vary. Good luck. If you need any help/advice, feel free to pm me, Ill help as best I can.

-Sean-