You can add up to an additional 7 retainers for an added monthly fee per retainer, and an additional retainer and double saddlebag space with the premium app sub, for a total of 10 max retainers. Combine the bank space (175 per, for a total of 1750 at max, 350 for base sub) with being able to send them off to gether materials (Provided you've leveled the appropriate gethering/adventuring job) and they're amazing time-savers and passive income sources. Recommend setting one retainer's job to your primary combat Job when you settle on it, this allows the retainer to hunt specific mob drops within the item level of the retainer's gear, and saves some gil and time getting some of the more convoluted mats.