I know the hiring supervisor's name. Is it okay to open the cover letter with "Dear Sir Full Name"?
"Sir Full Name" is only used when the person is a knight.
Use either "Dear Full Name" or "Dear Mr Lastname" (or "Dr Lastname etc."), or "Dear Sir" (without a name).
"Sir" only applies to men. "Madam" is the female equivalent, "Dear Sir/Madam" if you don't know which to use.