In the U.K. it should always be singular,
'Final' for 4 miles or less, 'Long Final' for 8 to 4 miles.'Short Final' is not defined,but generally held to be less than 2 miles.
It always slightly raises the hackles when a pilot/ATCO uses the plural, I wonder if the finer points of thr R/T lessons were wasted on them.
Yes, the runway designator should always be used (It's a last check to all parties that everyones singing from the same hymn sheet).