2) Wiring. I plugged the supplied cable into the back of the radio, plugged the steering wheel controls into the Y-cable, and routed as you can see below (red line). BTW, the Y-cable still allows you to use the steering wheel controls and is plenty long enough to reach the armrest, but barely.
3) Placement. I placed the USA SPEC inside the armrest console for access to the RCA inputs, and also because there is absolutely no free space elsewhere to put the damn thing out of site. About the only other hidden place is where the circle is on the below pic. I did have to drill a hole for the wiring to feed through, use caution when drilling and check behind the plastic.