I would focus on how the symbolic nature of the beast is used to terrify and disgust us as the reader. By using the beast to demonstrate how the boys slowly return to our more primal instincts, Golding makes our stomach turn.
To pick up on #2, the best way to approach this essay would be to focus on how characters perceive/react/respond to the beast and how these responses can be compared or contrasted. What is interesting about the beast is that it reflects more about individual characters in a sense than it does the "beast" itself, therefore your essay will want to draw out what the beast shows us about characters such as Simon, Ralph and Jack.
The beast is within us all, as Simon recognized immediately and ultimately died for knowing. Jack knows this as well, but uses the fear of the beast to manipulate the little ones into behaving and choosing his camp over Ralph's for safety in numbers. The beast rears its ugly head to take the order and logic of the tribe, thus murdering those who represent order, logic and sensitivity: Piggy, Ralph, and Simon. Only Ralph escapes as a result of the island fire drawing the naval officer's attention.
While your focus is on character analysis, you will probably need to give some background from the plot as to how "the beast" evolves to a tangible existence for the boys. Maybe you could start with a brief description from Chapter 6 of the meeting in which the boys describe what they think "the beast" is. From this description, you can launch into a discussion of how, as a Dean Koontz character declares, "Perception is reality." For, each boy sho describes "the beast" is convinced of his own description. Even Jack is insistent on his own perceptiion: There is nothing on the island because he has not seen it.
Only Simon, who ironically cannot articulate anything about "the beast," recognizes this "beast" for what it really is, the evil inherent in each boy. (This is why each boy envisions "the beast" differently.) Simon's knowledge is intuitive, and, therefore, impossible to verbalize.
Most of the boys perceive "the beast" as something outside themselves because they have fallen under the evil influence of Jack and Roger. Ralph, like Simon, senses "the beast" in the end of the novel as he weeps for the loss of innocence when the officer rescues him from the savages.
---So, build your thesis on the emergence of "the beast" as an entity and the effect this beast/evil has upon the other characters. Also, you may want to read the summaries and analyses of Chapters 6-12 on the site below as theses will help you refresh your memory and generate some ideas for you.