Yes Sir ;)
yes, Sir is a male prefix or form of address
You spell sir as in mam sir.
You will only ever capitalize sir when it is a title. Example: Sir Elton John You will only ma'am when it is the beginning of a sentence (it is never a title). Example: Ma'am, you are dismissed!
You capitalize the word Dear but only sir if its his name ex. Sir...Babooshki?