I don't see any images??

 

What harnesses are required and recommended? Look on Crutchfield for the matching wire harness.
Will the stock amp and sub still work simultaneously with the new ones? Yes but I don't think you will want the stock sub playing after you install aftermarket equipment so just cut the subwoofer wires coming out of amp.
What functionality will I absolutely lose/ not worth it to retain? Steering wheel control.

 

 

So I don't think I've been a member long enough to post pictures, sorry.
I looked at crutchfield, and they said the wiring harness is the 'Metra 70-1730' one. It also says it retains factory amp, but how does this affect me since I don't care to retain factory amp functionality? (It only powers the factory sub, correct?)
I have been seeing there are steering wheel control interface kits, these don't work?
Also wondering what I'll lose as far as the hands free system, HVAC, and other displayed items.

 

Your factory amp powers all speakers including your sub. You have to decide whether to your going to power everything aftermarket or retain some factory power to power some speakers. I recommend choice #1(bypass). Steering wheel control modules do work so if that's a big thing for you go ahead and purchase one but to be honest it wasn't for me seeing how the touch screen from my double din Kenwood is literally 6 inches away from my hand on the steering wheel. Hands free will be gone but your new HU should have something similar and HVAC control will remain the same in the upper dash screen. Here are the components you will need to make it all happen. Good luck.
Metra 40-HD10 Antenna Adapter
Metra 70-1730 Receiver Wiring Harness
Metra 95-7805CH Dash Kit

 

 

 

Nope. If you're buying a new head unit then you will run them separately from the back of the HU.

 

Install your head unit and run RCA's to the sub amp then wire up your new subwoofer from there...You can disconnect the wires to the factory sub. Are you planning on doing this yourself and more importantly, is this your first install?

 

Okay, easy enough. I didn’t know disconnecting the factory sub would be so easy. No not the first time, but the first time I’ve dealt with anything more than a basic factory system without amps and subs.
About the Usb and AUX in the center console... Where do they come from? straight from the back of the factory stereo? I’d like to rig them back up for the new AUX and USB connections for my HU.

 

you will have to run the new cords through the center console. The existing accessories are not usable with a new HU once you remove the OEM stereo.

 

 

What part of California are you located? If you're in my neck of the woods I might be able to free up some time to help you out. I'm kind of a car audio geek.