As regards the central question of your essay concerning how symbolism and allegory are used in this excellent short story, literally hundreds of questions have already been asked on this, so if you search in this group you will find plenty of answers. The key to writing a good hook statement at the beginning of your essay is establishing a connection between the theme of the story or text you are writing about, the essay question and the audience of the essay. A hook statement should be able to grab the attention of your reader and draw them in to read the rest of your essay. A great way of doing this is coming up with some sort of statement that relates to the theme and expressing it in ways that the reader can relate to. If we consider this brilliant short story, the key theme is obviously about the impossibility of escaping or cheating death. The way in which Prince Prospero tries to do this by locking himself away in a castle, and yet still the Red Death enters, clearly demonstrates this. A good hook sentence to open your essay therefore might be something like:

Man, throughout his existence, has raged against the inevitability of death and has done everything he can to try to escape it. In "The Masque of the Red Death" by Edgar Allen Poe we see how yet another such attempt is doomed to failure through the use of literary devices such as setting and symbolism.

Obviously this is just an idea to get you thinking, but hopefully you can see how the opening sentence provides a general hook and a link to the reader before you then go on to state your thesis statement and signpost your essay. Hope this helps and good luck!