[Ronbo]

You're best getting RAM from an outside vendor. They'll even tell you that at an Apple store.

I believe WiFi is pretty much universal, as long as it's using the 802.11 standard. Current is 802.11n. I use an Airport Base Station just to keep things simple, but you don't have to.

For compatibility with MS Office, I use OpenOffice. I exchange Word and Excel files with PCs without any problem. Get OpenOffice v. 3.0 and you won't need to use X11 to run it. It's free at openoffice.org.