Include an introduction and a conclusion no matter which method you choose to structure the body of your essay. It is often helpful to write the introduction and conclusion after you have written the body of your paper. A good introduction will introduce your subject in a general fashion and then begin to narrow gradually, ending with your argument. Think of it as a map of the rest of your essay. The conclusion should return to the ideas with which you began your essay and restate your argument. It should leave your reader with a summary of your main points as well as your argument.
Hard to say. I used to use this structure as my bible but I felt some of the comparisons I was getting back were very simplistic. Basically some students were only pointing out obvious similarities but failing to comment on subtle differences between the texts. As long as you bear in mind that subtle differences matter every bit as much as similarities, you should be fine to use this structure. This example might also help (it’s cultural context rather than theme but the same basic principles apply) http:///2013/12/sample-comparative-link/