Bought a Headunit, Few Questions about Accessories

I just bought this headunit for my 2000 Dodge Ram 3500 Dually. We use the truck for trips buying and selling antique tractors and I wanted something with built-in GPS, built-in phone, and a backup camera for hitching up to trailers.

My questions are:

1) What kind of harness plug will I need to purchase to install this headunit? I have searched and searched and I have found nothing.

2) What are some good backup cameras for me to purchase that will work with this headunit. I'm using it mainly for hooking up to trailers. I would rather have one that fit into the tailgate handle because I like the smooth look and the angle of the camera, but I am not sure if one is made for that year truck. Soo....what camera should I go with and how will it mount?

3) The headunit should come with a bluetooth microphone for the cell phone feature. This truck has the LOUD Cummins Turbo Diesel Engine. Regardless of that, my friend has this same headunit and mircophone in a small car and you can NEVER hear him very well at all. Is there a better microphone out there I should buy? I know with most factory bluetooth systems, I can usually hear the person perfectly.

Just to clarify, the headunit is a Kenwood Excelon DNX-690HD

Metra 70-1817 is the wiring harness you will need. Im not sure on other universal cameras but the Kenwood CMOS-220 works well with your HU

Yeah, I know the Kenwood would be the "best fit" but how does it mount?? It is n't a license plate mount, and since there isn't a "factory place" for the camera I don't know how I would mount it. Also, how does the camera activate since it shows only the video plug? I don't care much about having that big round button to activate it. It looks a little tacky. I'd rather it activate by putting truck in reverse.