Seems pretty clear to me - get the N800.

All the other devices you listed are either not available, lacking major features (WiFi or BT) or designed for the Japanese market (and I'm guessing you're not a Japanese speaker/reader). The SL-C1000 has only a 640x480 screen so would be a significant downgrade from the 770/N800 and would seriously compromise internet usage.

You don't have to shell out for the case and keyboard, that's your choice. Certainly the keyboard is of questionable use unless you are a prodigious IM/Email user - my BT keyboard that I thought I would use a lot is very rarely used. A case on the other hand would probably be a very worthwhile investment.