1. No, at least in the US. Not until on a published segment of the approach or with further ATC descent clearance. Some may take cleared for approach as an inferred clearance to descend to the published altitude at the fix, but its not. Again, this applies to the US.
2. Likely yes unless the fix is quite a distance from the runway and losing the extra 3 thousand wouldn't be hard.
3. Remain at 6 until receiving a clearance for lower. Not so much to your example but it comes down to technique if one joins the GS further out and cross checks altitude at published fixes or if they descend to the altitude specified in the clearance or on the chart.
Pilot viewpoint.
As to number one, it changed to a published segment due to a crash back in the 70's I believe, perhaps TWA.