Should I daisy-chain extension cords or buy a longer one?

Buy a longer cord instead of daisy-chaining. Daisy-chaining introduces two points of failure, increases resistance and heat buildup, and if cords are different gauges, the thinner one can overheat. If you must daisy-chain, use same-gauge cords (12 or 14 AWG), keep them fully uncoiled, and keep the connection off the ground and away from rugs.