To structure paragraphs, it's useful to use the T.E.A.S. method. T for thesis, E for evidence, A for analysis and S for summary. A thesis is like a 'signpost' for the marker, it tells them what the paragraph will argue. Each paragraph should cover a single core point. Then, evidence (E) should back up your thesis claim. This is where quotes should be from the text you're analysing or commenting. This is also where your exterior knowledge comes in, e.g dates. I personally find analysis (A) most difficult because it is where you join your evidence to the question and analyse it. It should be the longest part of your paragraph and should clearly answer the question being asked. Finally, the summary (S) should be an overview of the analysis given and offer a sort of conclusion to the paragraph.
The number of paragraphs you choose to have depends on how many points you are making. These do not include your introduction, which should introduce in brief the points you will be making, or your conclusion, which should answer the question and give your final opinion. Markers should be able to get a good idea of your opinion by simply reading the introduction and the conclusion.