SR Head Unit Upgrade

Looking to upgrade the non-GPS head unit I have with a second-hand OEM Entune Premium one. Both are non-JBL.

What does "Pre-Programmed to VIN" do for the head unit? What would happen if the unit wasn't programmed to your particular VIN?

Is there any way to purchase the wiring harness without purchasing the head unit? Whether it be through this company or elsewhere?

When upgrading from a non-GPS to a GPS-enabled head unit like the Entune Premium, what can I do to enable the GPS on the Premium one? (Though GPS isn't the main reason I'd be getting it. I've survived without GPS across all my vehicles).

Can I expect the HUD near the speedometer to work seamlessly with the upgraded head unit? I've noticed Tacomas with the upgraded head units have more information such as song playing, directions, etc. I dont have that.

That's all I can think of for now. What else should I be wary about?

 

I thought about upgrading mine as well so I'm for the answers

 

Anyone have any input on this?