Renault megane mk3 2012 stereo and head unit display upgrade

So here is my idea, I digest the shocking stereo/speakers set up renault has churned out in there latest set of cars, my one included, my issue is I bought my TomTom edition megane because of the safety of a built in sat Navy over using a stand alone unit which are very easily stolen, so my issue is if I change the standard stereo I loose my TomTom satnav, here is the dilution I have been toying with, I am planning on getting a set of Sony speakers, using my pretty much new Sony head unit which has built in Bluetooth, USB and aux input as my head unit then buying a half decent tablet for my display up top, I have at a guess about six or seven inches of usable display area, so I'm going to buy a spare surround for me to mount my tablet to, running wires to charge it and sitting it in such a place the power button and such are accessible is going to be difficult but doable, that or I will set the tablet up to turn the display off after a minuit of inactivity or such, I will buy the adaptor to make my stalk work from my steering column, and download a sat nav app off the android market, I have a few I like and have used before, also I might play with the idea of getting a digital display read out like g sensor and such but that would just be a gimic in a 1.5 DCI model, this would give me the best of all world's as I can change the head unit as or when anything goes wrong, I could wire in a sub wooofer or amp the door speakers if I so wish, but not loose the display unit.

This is my theory at the moment, any ideas or additions would be welcome, if I go ahead with the project I will keep you guysupdated with pictures and such so you can see how it goes

Renault megane mk3 2012 stereo and head unit display upgrade