만이요 is not generally used often in good korean expression,so u dont need to worry about it,,,just remember the meaning of 만 is "only",,,ok
뿐이요 is also not a good korean expression,,,뿐 also means "only",,,,ok,,,,,u should remember that korean is a language not only of words ,but it is like a beautiful poem ,,,the sounds must be in a proper beautiful sense,,,so we cannot use any words in any way ,,using of words properly comes only after some time,,,ok
이나요 is often used,,it is important,,,ok
good luck,,,please wish good luck for my chinese !!!