Ok a few important questions about N80

1. Can you transfer video's (after encoding) to the phone, such as full length movies and then playback them? Because i can on my O2X3, and thats a pretty old phone.

Yes there is a software Smart Movie By which u can convert whole DVD and send it to ur phone (If u have that MEmory)

2. Also, does the flash work like a real camera flash? I recently looked at the sony ericsson k800i and saw the flash is simular to one of a camera, but am not sure.

Persnally i would say NO.
The flash really woks in the complete dark
but in indoor it does not work properly
flash is better then 6680 but little less as to N70 (only Flash)
in Macro it work well
You can't compare with Camera

3. Can you install software such as image editors, video editors, ring tone composers etc..?

We already have Image Editor (In Bulit in the Phone and Video Editor too)
Ringtone edition will be soon avb, as the companies are inroducing the 3rd S60 Softwares.