Yes. You should capitalize all religions, as they are proper nouns.
Yes, you should capitalize "About" in a title.
Yes, the Sacrament of Holy Communion should be capitalized as it is a proper noun referring to a specific religious ritual in Christianity.
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.
no
No
No
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.