Do I need a full 5-piece set or just one pair?

Verified-purchase reviewers consistently report that a 10-inch curved-jaw pair handles 80% of locking-plier tasks. Sets earn their keep when you regularly switch between large clamping jobs and detail work (e.g. extracting stripped fasteners with a long-nose pair). If you're a casual DIYer, one 10-inch curved-jaw pair is the consensus starting point.