It is important to remember that this is a rough sketch by which to write your essays. If your topic is quite complicated, then you may have infinitely more evidentiary paragraphs than three. Furthermore, you can expand your individual themes, as well. You can write two or three paragraphs in support of "theme 1" (or Body Paragraph One). The most important thing to remember here is consistency. If you have two or three paragraphs in support of one piece of evidence, then you should have the same amount of paragraphs in support of all sequential facts.
While the body of the essay should generally include objective information, the conclusion should include one or two sentences articulating the author's opinion. This stance should not be conveyed using an "I" statement, which is usually not recommended in formal writing. For example, a sentence relating to the thesis statement comparing life in the city versus life in the country could be, "For these reasons mentioned above and others, life in the city is more advisable for individuals for whom a better quality of life is non-negotiable."