Q: Do I need the fore arms, the aft arms, or both?

It depends which bushings failed and what you want from the car. The Lateral Fore arms carry two spherical bushings and a ball joint each and anchor the strut, so they influence steering feel most directly. The Compliance Aft arms sit rearmost with one spherical bushing and one spherical ball joint, controlling fore-aft wheel movement. High-mileage cars usually benefit from doing both. Precision-focused drivers should run the full set.