One question I would ask is whether the advantages you describe are actually disadvantages for inexperienced writers. Does having a mechanical thesaurus help you learn to use words correctly and expand your vocabulary? Or just increase the chance of misusing words? Spell-checkers can correct typographical errors that cause misspelled words, but will not catch mistakes such as typing "sad" when you intended "dad"; they may even lull you into a sense of false security, leading you not to edit your work carefully.
More significantly, if you could give us a sense of the assignment, we could probably give more detailed responses. Is this for a high school or university class? Is it supposed to be about typewriters? Writing technology? A specific genre of essay?
If your focus is "why word processors are better than typewriters" you might want to change your first sentence. Currently, the rest of the essay doesn't really follow from your opening.