Yes, there is a cinema mode. You can enlarge/reduce the "screen" continuously. Sound is of course limited (but not bad). I can't give you exact information about the maximum running time, but I have watched films for 2.5 hours at a time.

Virtual desktop works very well, allowing you to see your PC screen in the headset. Steam VR games work
Headset battery lasts at least 2 hours, good controller autonomy