OK that sounds good. Just a couple of points to add.

You might find you need the flash less that you expect. I have the D300 which has a very similar sensor to the D90 and 3200ISO is quite usable. If you want to use the diffuser thing a lot then remember that one comes with the SB800 which might make you prefer it over the SB600. Stick with a compatible Nikon flash - the Nikon system is really sophisticated and you can't be sure that other manufacturers flashes are really compatible.

For your memory cards - remember we're talking about SDHC here, not Compactflash. I wasn't aware that SDHC class 6 could do 30MB/sec but then I don't use Sandisk