I think your RNS should be a late enough model to allow this no problems.

Plug and Play - should be. but you will need to add a GPS doodaaa, the RNS maynot be compatible with the factory fitted DAB module though. Phone kit should actually be better once RNS installed, MDI will also be better due to screen size (the RCD310 only has one line of text when scrolling through MP3's on Ipod.

I am sure there will be some ICE genius along soon who will give you a definate answer on any coding required.