Discountinvestigator,
1/-Each *reverser* is made of four blocker doors on the CFM. Principle is the same for the IAE. What you need to know is that the amber light only relates to its engine.The unlocked/unstowed amber light is either a malfunction -in which case you'd get an ECAM warning - or the transit phase of the reverser deployment/retraction on that engine. The other T/L position has no effect.
2/-The most accurate word is *latched*, really. Each of the blocker doors has a latch that would keep it in the *stowed* position. The *locking-out* of a reverser involves blocking the deployment, both by mechanical and elctrical means. Depending on the models, in a locked-out thrust reverser, you'd get an amber light (meaning a disagreement between the T/L demand and the state of the reverser, or not -don't know why, whether is software or electrical...)
3/-The call with my airline is "Reverse one only green", as per SOPs. Some airlines prefer "Reverse left only", which gives, IMO a better clue for the side of an expected yawing moment, but it's very small.
4/-The *Reverse Fault* is inhibited at take off until passing 1500 ft height.
5/-Already answered. Yes.