Confusion wiring up my Sony XAV-AX8100 to my 2017 Honda Pilot LX

My factory receiver is the smaller display version, and doesn't have carplay or android auto. So, I'm upgrading to the Sony XAV-AX8100.

I bought an install guide from Crutchfield, but it either has information I wasn't expecting, is missing info, or is confusing.

Basically, to answer the below questions, I need the pinout of all of the wires coming into the Honda factory wiring harness because it seems I will have to tap into some directly as they didn't come into the Metra wiring harness I got.

*** Question 1 - The backup camera ***
The Crutchfield guide says "Reverse (+) - below dash fuse box, 14-pin plug (D), pin 21 - brown".

I have a wiring harness for this. Ground to ground red to red, and then it has RCA cables coming out of it. I capped off the Red and White, and the Yellow just goes into the Yellow video-in jack on the receiver.

The Sony unit has a purple/white-stripe "Reverse In" wire. If my vehicle already turns on the factory backup camera when I shift to reverse, wouldn't this wire be in the incoming factory wiring harness? Which wire is it?

*** Question 2 - The steering wheel ***
The Sony unit has a 3.5mm input for this, and included a 3.5mm wire with 3 connections - Input 1, Input 2, and Ground. Where do I connect Input 1/2 to the incoming factory wires?

Also, with this, it seems that there is no need for a Metra Steering Wheel Control Interface, right?

*** Question 3 - The speakers ***
Googling the Pilot LX, there is come confusion about exactly how many speakers the LX has. It seems there are 6 speakers, though.

The Sony unit only has a 4 channel output. But I figured I could just wire the front 2 dash tweeters and the front 2 door speakers in parallel with the first 2 channels. Then I could hook the 2 back speakers to the 2 back channels. There is a sub - which I am hoping maybe the car has a built-in amp already for?

Any help/ideas with this would be much appreciated.

Thanks!!!