What is the role of a flight control computer during a steep approach?
On the Airbus 318, it appears that the flight control computer does more than just monitor and handle annunciators. 


  In March 2006, the European Aviation Safety Agency (EASA) certified a modified control software enhancement to the Airbus A318 designed to allow the aircraft to perform steep approaches. The aircraft is the largest commercial aircraft certified by EASA for steep approach operations. The software modifies the control laws of the aircraft when the steep approach function is selected by the crew, by automatically deploying some of the spoiler panels to provide additional drag when the aircraft is in the landing configuration. It also provides alternative aural alerts to the crew and modifies spoiler deployment automatically below 120 feet (37 m) on landing. The A318 steep approach procedure allows the aircraft to perform approaches at descent angles of up to 5.5°, as opposed to the standard 3° for a normal approach.


A318 Wikipedia

The answer to your question #2 can be found in the aircraft operations manual.

The answer to your question #3 is that an aircraft can stall at any attitude and configuration. A stall is when the critical angle of attack for the wing is exceeded.