Yes you can. People do it all the time. Its best to give exact change. Your mail carrier will put a stamp on it for you
Yes. My mom used to do it all the time and the mailman took care of the stamps. We lived in the country and the local store charged double the stamp price and sometimes they were just out.
No do not do that, never ever put cash money on the outside of a letter. Ever. It will be returned to sender amd it wont have your cash on it
Thanks! Your answer is awaiting moderation.