Hey i have an archos 70 same gen as the archos 101 couldn't you just use that for your android tablet setup. What i mean is this, the archos gen8 tablets can output to a tv or monitor via hdmi although it is big enough to be a good sized monitor for ya. when outputting via hdmi The tablet would then act as a large track pad like a laptop. That tablet also has a full size usb host that you could use for your hard drive. you may need to supplement power but you can do that with either usb with that y cable that comes with your external hard drive or inverter for the hard drive. then you could use the attrix or other phone to provide internet connectivity and/or you could also use it to control or output to the tablet via vnc.
Those are some ideas. As far as power, how to shut down if the device is in your car, you could use the tasker app and setup a profile to handle turning it on and off when it is plugged in or docked; software wise even make a shortcut widget to automate that process for you. As far as front ends i would use a car dock app like custom car home or car dock home v2/3 to give you that front end feel and give you easy access with larger buttons. then you can use vlingo or google voice to interact with your device by your voice. That was a mouthful hopefully that helps. You can visit my website in my sig to get some ideas of what apps to run and what have you.