2002 XK8 Convertible. I would like to put in an aftermarket stereo with a CD player, Bluetooth, iPhone 8 compatible, retain steering wheel controls. I am also hoping that any recommended systems would have an optional wiring harness for this car. And finally, is there a trim piece for this car that will look like a factory install with a single DIN stereo system?

 

don't recall of any plug and play system being available.
There have been a few threads on how it was done, so do a search, at the top of the page.

 

I know you are on a different side of the water, but that didn't stop the Pilgrim Fathers did it ??
This company has a good reputation over here, and supplies everything you need :

https://incartec.co.uk/Jaguar/XK8-Coupe

 

Or you can do what I did and keep the factory stereo and add a Bluetooth kit to get hands free phone and streaming music.

This pdf gives a very good overview of what is involved - its for the XJ rather than the XK, but they are practically identical.

http://jimroal.com/cars/X308Bluetooth.pdf