Replacing HU on 2001 CLK 55
 

I've searched this forum and have gotten some answers but I'd appreciate any insight you have to the questions below:

1. To maintain steering wheel control does the PAC SWI-PS Sony and Pioneer Steering Wheel Radio Control Interface work,and if so is the install difficult?
2. Can I buy a VW wire harness an just install or a a maaping out of the wiers needed?
3. I just plan replacing the HU and keeping all else stock, is there is there an issue with voltage and power giong to speakers that I need to deal with.
4. Lastly, I'm considering the Pioneer DEH P700BT, JVC KD AVX44 and the Alpine IDA X305, any recommedations on those?

Thanks for your help