What worries them about Caesar is the fear that he will begin to think he is superior. They believe he will become corrupt and act as a dictator. He's a bully who is worshipped without cause and they fear he will hold too much power.
William Tweed was considered to be the most corrupt politician.
D is incorrect. William Shakespeare was never knighted by Queen Elizabeth I
It means to not only think of your own interest but also to the interest of others.