I recently installed Android in my R170.
Forget CAN Bus, R170 does not have the correct functionality on it's Body CAN.
If you look at my thread in Performance Mods you will see how complicated it gets, especially as I added a Steering Wheel with buttons.
Sat Nav will be very accurate even without a speed signal, the only other reason for speed signal is to increase volume as speed rises.
My Android functions perfectly without Speed Signal.
Reverse Camera, I just used the Video Phono Lead that also has a separate core to take a +ve Supply from the Rev Lamp Bulb and connects to the Back Up Lamp + on the HU, and the Video Cam Phono hooks in to the relevant H/U Video Input.
I would not try tapping Shifter, AFAIK
the (Facelift at least), Auto Shifters are working on a Powertrain CAN "signal" for PRND to TCU rather than a hard wired 12V output.
I have also installed these units in later MB Cars which have several full function CAN's, Body, Chassis and Powertrain, and they are soooooooo much easier to do, because the CAN Decoder does everything for you.
The R170 is however "old skool" and so needs a lot more hard wiring