I don't think you are correct. My Vietnamese wife says that "ư" is used to indicate a question, but it has a different inference to "khong". The question becomes a statement asking for confirmation rather than a simple question.
"Em yêu anh khong?" means "do you love me?"
"Em yêu anh ư ?" is more like "you love me, don't you?"
Whereas "à" is not used to indicate a question, instead it is used to show respect or deference.
I can ask a friend if they are well "anh khỏe không?" but my wife is quite assertive that when speaking to my father-in-law, for example, I must end the sentence with "à" - "Bố khỏe không à".
Also, I must add "à" after "Vâng" when answering a question from her parents with "yes" - "Vâng à Bố". It's about showing respect.
Apparently both are quite old-fashioned, or rather quite formal, but my wife feels that you yourself would earn more respect if you used these structures than if you didn't. They show you to be polite and respectful.