depends on your sac marks, which overall are worth 50 per cent of the study score, so it's still important to have been doing well, ie averaging high's to secure 35 plus, however, doing averagely in sacs and getting an A should still get you in the low 30's range.
i'm assuming you mean 10 mark questions since, there are no 4 mark ones and for 6 marks, you predominantly draw evidence from the document you're analysing unless you can concisely bring in relevant quotes or evidence to support your answer.
For a ten marker, i think more than one historiography quote would be advisable, so long as its relevant and you're not just adding quotes for the sake of having quotes. But more than one would be best, since, if you've seen last years exam, specifically asks you to "refer to different views" of whatever it is you're evaluating.
3-4 pieces of evidence would be sufficient i think.
the most important thing to remember is read the question. all 10 markers will require some evidence and historiography but some will be looking for "views" and others will be looking for "evidence"