Hi!
Sorry, I don't usually give out numerical marks because I am not a qualified teacher and not really experienced in giving out marks haha but I recond VCAA would give this a 6 or a 7 if if it were at the end of the year. You may be looking at a 7 for the SAC if you wrote this on the day- so that's a low B+ I think.. I am not sure about how Mulholland marks though.
SACs are technically cross marked but only if teachers put them out to be cross-marked - that is, if your teacher has any doubts/queries over the marks, they will put them out to be cross-marked. Otherwise, it would be unrealistic for teachers to be crossmarking 300 SACs in one-day (that's right, crossmarking/moderation only takes a day). If your SAC is cross-marked, the crossmarker's initials will be written down on your assessment/criteria sheet and if the box is left empty, it wasn't crossmarked.
You should analyse headlines and subheadings if it's worth analysing - that is the general rule for most things in English. If you have something interesting or worthwhile to say, say it. Otherwise, analysing headlines just because you think you have to will ruin your whole piece. Whether you analyse it in a separate or same paragraph depends on how you structure your paragraphs - whether by arguments, chronologically, by techniques/devices or by key players/stakeholders. Again, like I said in the comments make sure you have one approach and try to be consistent.