Can I use this sign to mean 'congratulations'?
While it conveys a similar celebratory feeling, it specifically refers to the action of a high five. For 'congratulations,' there is a different, specific sign where you clasp your hands together and shake them.
Do I have to make a loud clapping sound when I sign this?
No, making a sound is not necessary in ASL. The visual contact between your hands is what conveys the meaning, though a light, natural tap is perfectly fine.
Is this sign appropriate for formal situations?
Just like the physical action, the sign for 'high five' is informal and casual. It is best used among friends, peers, or in relaxed, celebratory environments.