I was wondering if the unit of measure for other settings such as RTH altitude or max altitude, do they switch to imperials or remain metrics?  Thanks in advance.

Yes they remain metric values.
Internally, the aircraft uses metric and then converts many data elements to imperial when we select imperial. But as you note, RTH altitude, max altitude, max flight distance and any other setting that show their range in meters such as these rema in meters always. So set them accordingly!!!