Ok here's where I'm sitting at, with 7 total Retainers, to show why I'm worried with space. Now yes I know a lot of people are just saying, "sell what you don't use much, or what you can get at a vendor." The Vendor stuff I can see, but I still like having it on hand so I can just Search Item and know exactly how many I got and where. But here's my breakdown of stuff:

Retainer 1: Ingredients, 140/175
Retainer 2: Stone/Metal, 158/175
Retainer 3: Wood/Lumber, 40/175
Retainer 4: Leather/Bone, 82/175
Retainer 5: Cloth, 38/175
Retainer 6: Reagents, 109/175
Retainer 7: Materia/Dye/Gardening 50/175

Now yes I have plenty of space when you just look at the base numbers, however I have yet to get hardly any of the lvl 50 ARR items, and still have to go into Heavensward and Stormblood content.