I can't answer in details to each questions, but here's an overview:
Android is like a middleware that runs on top of Linux.
See Android System Architecture
Linux takes care of the low level things drivers, network stack... and Android is taking care of the high level parts.
So the way I understand it you would probably be able to run Android on top of Debian for ARM, but applications such as OpenOffice won't run in your device.
If you only want to run Debian on the phone with X server, it might be possible if you find a Debian port to your phone. In that case, you should also be able to run your applications, but you may need a keyboard and mouse to use it...
For the USB to Ethernet Adapter it should be possible, as long as it is supported by the linux kernel.