HELP? Upgrade head unit to a 2din dvd system?

I have a 04 Avy with boss and DVD system for the rear. I want to upgrade mainly to add a backup camera/Bluetooth and use my iphone 4S.

I think im buying a Pioneer AVH-200BT system. What else do I need to purchase to for this install? I have installed a couple stereo's in the past. But that was simple. I want to include steering wheel controls also. Can someone help me out. I have looked on a couple sites but im over whelmed as what I need to purchase? 

Have you tried www.crutchfield.com.  They will tell you everything you need.

Also www.pac-audio.com has some good things.