Fingerprint sensor will be in/on the screen.
It wont
At least, from the firmware leak theres nothing indicating a « under display » fingerprint sensor, theres even rumors it might be completely replaced by infrared facial recognition.
the front looks okay but the back better be metal
That wouldn’t allow wireless charging integrated to the back of the phone (which is rumored to likely happen for this one), I personally think glass would give back that premium feeling from iPhone 4/4S