Welcome to the world of E53s

I "like" to rescue beat down BMWs myself and my soon to be parted out E83 has 375k on it and purrs. Sounds like the PO at least did some maintenance which is much better than where I usually start from.

FCP = Warranty = Don't worry about it.

Delphi is a reputable brand and I wouldn't hesitate using them in my vehicle.

"Black Bastard" was doing the temp spiking to hot and then coming back down and it wasn't overheating so I ignored it and it hasn't happened in a while. Mind you there was no error code regarding coolant temp (That I remember anyway)

The temp sensor in the lower hose is something that goes out regularly so I would start off there. I bought an Amazon cheapy for one of my vehicles and it worked just fine.

Personally I don't get too caught up with the whole OE/OEM thing. Many of the "premium german" parts that I've bought have MADE IN CHINA stamped right on them so paying top dollar doesn't necessarily guarantee you are getting good quality either.