AFAIK, the harness is in all SCs whether or not the VMM is installed, so you should be ok to run without it if you want.
As for a double din, there was someone here that did it, but I recall one owner went so far as to mold in the bezel so it looked original.
I wanted a 7" screen, but opted for a loaded single din with pop-out display. That way I kept the same install basics and still enjoy a larger display. Be aware there isn't a lot of room behind the head unit, so be prepared to remove material if the unit you use has a ton of leads. Mine has more than two dozen, but
I have 5.1 surround, GPS, 3 cameras, hands-free calls, 9 speakers, and 2 zones, not to mention of course radio and DVD capabilities. As well, sticking w/single din means the VMM remains.
When I start the car, the head unit extends the display (articulated), and when shut down, the display retracts, giving a near stock look.