Congratulations! And welcome to MobileRead! I've had my 900 about two weeks now and am it has become my go-to reader.
The 505 screen is definitely better, but the 900 is not bad at all and it's features make it a bit more convenient to use.
In addition to Bremen's help above be sure and check whether you local library loans ebooks. Mine does and it's a wonderful way to read new releases without any cost at all (well other than taxes, right?
).
Enjoy!