I guess the 720×576 is Anamorphic as it was recorded on a 4×3 chip situation so the 720×576 should look a bit squashed in 4×3 mode. When stretched out it will be 16:9 and looking correct.
Had a lots of problem when using FCP with video from a Sony Camera which had 4×3 sensor but was actually 16:9 anamorphic.
I will leave some of the Pro’s to answer the other questions as maybe my answer may not be exact///