It is proper to start a sentence with the word "it." However, the referent for "it," in other words, what "it" is, must be clear (unless, of course, you're writing creatively and intend to build suspense, e.g., "It came." "What is 'it'?" "The Balrog.").
Answer:
Consider the opening of tale of Two Cites by Charles Dickens . It was good enough for Dickens it should be good enough for the rest of us.
"It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair..."
NO
No, a sentence can begin with any kind of word. The first letter of a sentence is always capitalized to mark the start of the individual sentence, not because the word is a proper noun.
Yes.
Yes, it is proper English to start a sentence with the word "oh." This interjection can be used at the beginning of a sentence to express a range of emotions or to call attention to something specific.
No, because "and" is a conjunction, which is a word that puts together phrases and clauses to create a sentence.
No, because "and" is a conjunction, which is a word that puts together phrases and clauses to create a sentence.
No, the word cholera does not have to be capitalized unless it is the start of a sentence or part of a proper noun.
No, unless it is the first word of a sentence or part of a proper noun.
No, you should not. You should only capitalize a word when it is at the start of a sentence or when it is a proper noun.
You can begin the sentence with a modifying adverb clause. "With the proper care, many mistreated dogs will recover."
No, "diabetes" is not capitalized unless it is the first word in a sentence or part of a proper noun.
No, why should it be? Well if it's at the start of a sentence, but really, how many sentences start with the word example?