How can I calculate the cabin pressure following a decompression?
You should read through this paper it outlines a lot of great info on calculating valve size for cabin outflow valves in pressurized aircraft it also addresses your second point (to an extent) on the flow rate of compression systems. The issue you will encounter is that the calculations will only hold for a controlled situation i.e. a situation where you have precise control over the valve (hole) size and can account for small leaks.

In the most generic terms you can find the calculation for flow rate through a hole in a pressure vessel here. 

Your specific example is going to be a bit more complex since after a cabin pressure failure the plane will begin a descent rapidly to 10,000ft. so your exterior pressure will be rising as your interior pressure drops (you will need to factor that in to make the above solution a complete result). You also need to consider the airflow over the airframe its self since you are talking about a situation where the aircraft is in flight you have some fluid mechanics to play in as well.  

Its called explosive decompression for a reason, its going to happen very very fast.