Don't consider these as answers. I was never an English major and these are questions for an English major. I actually know someone who wrote a college senior thesis on "Paradise Lost" but unfortunately she doesn't use email. You may wish to correct your typo, "thunder bath" should be "Thunder hath."
For "does Satan feel equal to God," my understanding of the difficult phrase "And what I should be, all but less than he/Whom Thunder hath made greater?" is that Satan feels in Hell he is capable of being almost, but not quite, equal to God.
For "why is the power of reason so important," I would guess there is some relation to the statement that is "the mind... can make a heaven of hell, a hell of heaven."
I can't address the first question, because the definition and classification of "semantic areas" is specialized and not common knowledge. Does your book contain a short list of names of "semantic areas?" I find the question puzzling. I don't feel that the passage you quoted really does say much comparing Heaven and Hell. Heaven is light, Hell is gloomy; Heaven is happy and full of joy, Hell contains "horrors." Many of the comparisons are implied--he says that Hell is far from God without directly saying Heaven is close to God. And he says that for himself, Heaven is safe, secure (the "Almighty... will not drive us hence") and a place of freedom--again without directly saying that Heaven is the opposite.
I wonder if your passage is really the one that contains the "antitheses," or whether there's something clearer, before or after it, that you are supposed to be looking at.