The plan for me right now is:
MK908 + Finless Rom ( Location Setting and Mass Storage Device )
Powered USB Hub
Touch Screen: 7" 1280x800 USB+HDMI
USB GPS Dongle ( BU-353 looks to be my best bet )
64GB Flash Drive ( Music Storage )
TPLink MR3040 Mobile Broadband Router + Work's Verizon 3G card for Internet. ( I already have the router that I carry in my backpack. I may consider getting a 3020 ( Same thing, but no battery ) for dedicated use in the car, and just have the USB port handy so that I can add and remove the USB stick as needed. I've tried messing with offline maps, but in my tests it still didn't seem to do what I wanted to without an internet connection.
Also looking into a USB ODB II input.
The thing that would be nice is if there was a way to connect your phone to the tablet to make calls. But really, I have a little bluetooth speaker on my visor that will work, or if I REALLY wanted to, I could get the grom unit with bluetooth. ( Or go a different head unit route, which I'm trying to avoid for now )