ClkAMG5

Picked up a 2004 CLK55 convertible a couple weeks ago. Amazing car, but compared to my DD which is pretty well optioned technology-wise, having essentially just an FM radio and CD player is a little disappointing. The car has the Bose sound system but no COMMAND, just the standard head unit and CD changer. Looking to swap in a double-din receiver with Bluetooth and CarPlay and have a few questions:

• Is there factory functionality (chimes, security, etc.) piped through the factory unit I need to be worried about?
• Is there a recommended module for these cars for keeping steering wheel controls (idatalink, etc.)?
• This seems like a longshot - but is there any way to tap into the factory mic for the Bluetooth function rather than running the mic included with the unit?

Any advice appreciated! Thanks in advance.