First Method:Arduino + Ethernet shield... this will limit the HTML size, so it wont look so nice... and I wont be able to control a lot with it.
The system will be controlling solenoids to lock and unlock doors as well, so I would appreciate the back up power.
I guess I will be running the Arduino Mega with an ethernet shield.
Does anyone know if CAT5 cable can carry 12v power?
I read somewhere else that the ethernet shield isn't compatible with the Mega. I didn't really pay attention because I don't have a mega, but you might want to look in to it.
Power over Ethernet runs at about 40v (if I recall correctly)so 12v should be fine.