My setup: http://www.youtube.com/watch?v=akJAqJL2aPg
If you mount it in the dash where the double din is located, you won't be able to use the camera to record your runs. With the car app I'm using, via the GPS it displays speed, elevation, etc during playback, so it'll help you fine tune your sessions.
Use dailyroads, it's a free app. This is what the screen looks like while filming and playing back:
You'll need one or two of these, as well.
That way you can adjust the volume without having to do it on the Tab, and with a lot more precision. It gets to be a pain in the a$$, believe me, having to reach for the volume control buttons on the Tab. I have 2, one for the sub amp and 1 for the 4 channel, mounted right under my arm rest and they are easily accessible.
The rearview mirror isn't really functional in my vehicle, so I pulled down. That's the add'l piece stuck to the windshield. I'm going to integrate the Tab mount's base to utilize the rearview mirror mount, so that I can pull it if I decide to sell the truck and want to return it to stock.
A keyboard really isn't necessary, IMHO. But I guess it depends on where you mount it. Swype works fine for what you need, and voice command does, as well.
You might also want to pick up one of these:
I hate having cords and crap all over the place, so I have this installed instead so I can power the Tab, my cell, and 1 add'l 12v device w/out having something coming out of the cigarette lighter.