How do I structure an answer to an essay that asks: "how far do you agree...."?

This is a great question because it can certainly be confusing when trying to make a clear and structured argument throughout your essay, while still attempting to show other interpretations.
The first thing we MUST ALWAYS do is read the question carefully! So, in this particular type of question there is often a statement that the question is asking you to respond to. Your analysis and close reading skills begin with the question itself. Think about what the statement is saying, what is the main argument? Look at the words and phrases the statement uses to make this argument, as well as the examples they use to support their claim. This is a similar structure you will use to either agree or disagree with the statement.
Once you have some ideas, you can then move on to planning the main body of your essay. You should have a rough idea of whether you agree more, or disagree more with the statement. You may find yourself understanding why readers may argue something while still believing your own reading of the text makes more sense, or in other words is more convincing, according to the examples in the text that stand out to you. This is great! you shouldn't feel confused by this.
This is how I would advise you to attempt to map out your ideas more clearly. It is only a broad framework to help your thought process, there is no absolute right answer! If you agree more with the statement, your main body may look like this:
The first and second paragraph/ or sections may focus on themes/characters that demonstrate why you agree with the claims made in the statement. In both sections, you may use detailed explanations that include an abundance of textual examples present throughout the whole text. This will make your justifications very convincing and assured! Then, your third section or paragraph may want to explore a counter argument. You may want to show how other interpretations are certainly possible, with direct response to the statement itself, BUT ULTIMATELY, your argument is more convincing. Here you can give a brief explanation for the counter argument, with a small example that shows you understand where this may be understood, but then state why this example itself is actually more revealing when read in the way you did/ or perhaps use another example that is present in the same scene/moment to show why the counter argument is overshadowed or undercut. Thus, its not as convincing as your own argument.
So, when you reach your conclusion, you can say that although there are moments that shows why the statement may be disagreed with, there is a more convincing amount of evidence to show that the statement makes a stronger argument which you agree with. You have tackled both sides of the argument, without losing your own clear reading of the text.