Leveling crafters with only 2 retainers is doable - you just have to actively manage items.

1) Can a material be purchased from an NPC for cheap? Most low level mats are sold at the guilds, in town, in housing areas, or by beast tribes (you just need to start the tribe questline to unlock vendors). Check an online database such as gamerescape, garlondtools, xivdb, etc.
2) Is the material sold for very cheap on the MB?
3) Will you actually need it for any upcoming crafts? Databases again help.

Only keep mats on hand that you will actively need in the short term, or are a pain in the butt to get. I semi regularly go on purges to tidy things up.