well, it sounds like you are looking to put lots of screens in your car..... May I ask what the motivation is?
Ill start with the 7" screens in the visors. why? if youve got a 10.4 in the dash, isnt the 7 inch screens kinda redundant? I dont see any need for them, even having who-has-bigger-balls syndrome, the 10.4 should be able to take care of that nicely!
it seems to be a 10.4 inch touchscreen would be able to handle your MP3 lists nicely, be able to play even street atlas very well, much less routis, do all your car music and navigation, your music video, your driving requirements. In this situation, I couldnt possibly justify a center channel, myself. two channel sound would be more than plenty. I myself am an advocate of no rear speakers at all, to have as much sound coming from in front of me as I can.
but you'll have a big screen in the back for the rear passengers, too. sounds to me like a great movie setup. I personally dont like 5.1, but it sounds like alot of people here advocate it. this sounds to me like an ideal chance to set up a wonderfully built true 5.1 setup, without being resricted by speaker locations in the dash, especailly with gauges and a 10.4 inch screen to also cram in up front.
so here is what I suggest:
I like your speaker location Ideas, but I would route signals differently. If there is a way to get the computer to control all this too, then its even more of a bonus.
youve got your front speakers, left and right. these, along with the subwoofer, would be your daily driving speakers. the front left and right for the rear passengers, along with the surrounds and center in the back, would be off. this would present an ideal music listening environment (or at least as ideal as possible). it would also let you isolate signals, if you had issues getting GPS to give directions while playing music and the like. youd have TONS of options, in this respect, and all still sonically ideal.
Then, for playing movies, the front speakers would be off completely. the five in the back would be on instead, and of course, the subwoofer which is always playing. this wouldnt have two front left and right speakers messing up the 5.1 envireonment, and everything is set up ideally for the two rear passengers for watching movies.
If you decide for whatever reason, to patch the video up front, its a smaller screen, probbaly not wide screen (im guessing) and if you arent in the back, then you are probbaly driving anyways, so whats teh point of being realistically in the world around.
If you were really slick with audio routing, you could have a movie playing on the rear screen in 5.1 while listening to music up front or GPS up front on the front two speakers. the subwoofer would share signal, it should be able to handle it reasonably well, although you might have to work on that a bit.
But thats what I would do, in this situation.