My shirt has 7.. but I don't know some could have more than 7. I think it is up to 9. I'm not quite sure.
Top Cat has a three button vest .
three buttons from the top if you are at a club or bar
Spread collars- With a bigger gap between the tips, a spread collar looks better with a wider tie. This city style is more formal, though it is common in Europe, and predominant in the UK.Point...
They are spares, you can use one if you lose a button from the shirt.
So if you loose one of the buttons you can sew a new matching one one.