A prompt set is built from evidence of what buyers actually ask: sales call recordings, support tickets, and the questions prospects raise before contacting you. It captures full conversational questions rather than search fragments, and is fixed in writing before measurement begins.
Twenty to forty prompts is sufficient for a single-service business; multi-vertical companies need more.
Include prompts where you would expect to lose, not only ones you expect to win.
A set derived from a keyword tool measures something, but not what your buyers ask.