Dont know if im posting in the right spot haha.

Im planning on installing my kenwood dnx 5120 in my 2000 lexus gs300.
Currently has the Nakamichi in there.

I'm looking for a harness to hook up the 5120. Ive called a few places and one place told me to bring in my stock headunit so they can look at the back of it for the harness, do I need to really bring it in or can I just buy their toyota harness ?

Ive looked at crutchfield and called them, they dont have a harness for a 2000 but a 99. Would I be able to use that ?

and after i get the harness is it just like hooking up any head unit ? anything different and what is the different if there is ? Ive been told i'd have to bypass the stock amp onto the head unit and my stock sub will not work anymore.

Any answers or tips, stuff im missing besides dash kit and harness ??
Will the OEM aristo double din dash kit work for this head unit or is it OEM nav only ?
anything will help. Please and thank you my fellow CL members =D