22 retainers across three alts - 8 on my main, 7 on my first alt, 7 on my third alt.

4 Lvl 60 Conjurers
4 Lvl 60 Archers
3 Lvl 60 Miners
3 Lvl 60 Botanist
1 Lvl 60 Fisher

The rest of my retainers are untrained.

My wife has a similar number of retainers but has 6 L60 DoW/DoM retainers, 3 L60 Miners, 3 L60 Botanists, and 3 L60 Fisher.

Do we need that many for mat and glamour storage? No. But once we started leveling alts, leveling retainers as well was pretty easy.

All this and I still have less than 8 million gil between all my alts. My wife has substantially more, tho.