I have 8 but it's not all about hardcore crafting. I am also a bit of a hoarder. My retainers are: 1 BTN, 2 MIN, 1 FSH, and 4 DoW. Fisher I usually just have out on ventures to try to get minions. The others are usually collecting crafting mats (when I have ventures). When I save up a bunch of ventures, sometimes I'll run a bunch of quick ventures. For storage, one retainer is for primarily processed items (ingots, leather, gems, etc.), two are for raw crafting items (ore, logs, fleece, ramie, sands, plants, waters, saps, etc.) and split up in no way I can possibly explain, one is for CUL items, one is for gear drops from dungeons and raids and old gear to be reused on new jobs (i.e. ironworks gear previously used for WAR now saved for DRK), one is for glamour items and furniture, one is for materia/demimateria and seeds/gardening items, and one is for special items (unidentified, coins, crafting gear from dungeons/raids/trials, favors items, etc.) and fishing gear/bait