The DVD player shouldn't be hard to do, especially if you go to an audio/customizing shop. I've seen plenty of vehicles including things from the C-class to the S-class with in dash TV/DVD and in the head rest.

That radar cruise control is a whole nother monster. I'm not saying it can't be done, but it's a lot of things that go into making that thing work and it's so new, you can forget about aftermarket, not saying that is the best/worst way to go. Now when ordering from the factory as you plan on doing, make sure you get all the components and beat it in thier heads that you want to install the whole system so that you won't end up with some parts and software that is not compactible. Good luck.
I'm tryign to find someone to install them air-cooled seats while keeping the original look. They said it will run me about $1800 a seat for the good quality seat that works better than most of them factory installed ones, MBZ quality leather that has been porforated more than stock for better air flow, and of course the blasted labor and wiring.