The audio cuts the end of laulatte, you can only hear 'laulat', as singular
This would have to say "you all" or similar to make sure that the second person singular is excluded.
Would "paljonko sinä laulat?" also be valid? Kinda like "How much do you sing?"
That is not something you would hear any Finn asking. Paljonko is a question you would use asking about how much something costs. It is asking for the quantity of something material.
You could ask that if you want to hear how much time does one spend on practicing the singing.