Finally upgrading to digital, could use some advise

[pafindr]

Hello everyone
I'm new to the forum and have been looking around quite a bit. I've gleaned a lot of info and want to thank everyone for their contributions.
I put together a shopping list and would like it if you could give some advise on what I want to purchase. I don't know a lot about digital so any help would be GREATLY appreciated.
What I'm using now:
Nikon N70
Quantaray 28-80mm f/3.5 - 5.6
Quanaray 70-300mm f/4 - 5.6
I do mostly do nature/wildlife/landscape but would like to slowly get into portrait.

My shopping list:
Nikon D90
Nikon 18-105mm f/3.5-5.6G VR
Nikon 70-300mm f/4.5-5.6G VR
Nikon MB-D80 Grip
an extra Nikon EN-EL3e battery
Nikon SB-600 Speedlight
2 - SanDisk 4 GB Extreme III 30MB/s


Now, Adorama has a grip that costs a bit less but I don't know if I should "go cheap" on it
http://www.adorama.com/INKMBD80A.html
Is the speed light ok or should I spend the extra money and go with the 800, 900, or something totally different?
I don't know a lot about memory for digital cameras so help there would be great too.
Should I add a diffuser to the list? If so what type would be good?

Thanks a lot for your help!
pafindr