No. E-mail is a common noun, so it does not require a capital letter.
No, except at the beginning of a sentence because it is n ot a proper n ou n.
Yes, "Kind Regards" should be capitalized as it is a formal closing in a letter or email.
Yes, you should capitalize "About" in a title.
Best should be capitalized but wishes should not. Thus becoming: Best wishes.
it depends , unless you want to
Yes, you should capitalize the C in Century.
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 should capitalize Colosseum when referring to the specific ancient Roman amphitheater in Rome.
Yes, you should capitalize "The Rotunda" as it is a specific place or location.
It should not be capitalized.
You should capitalize "Musical Theatre" when referencing the specific genre or art form.
Yes, it is correct to capitalize "Should" if it is used in a title as it is a noun in this context.