If your inventory and retainers' space are really that clogged up already, you can definitely afford to slack off on the crafting and gathering classes, so you don't have to worry about hoarding materials as badly. You can take your time with those through dailies like Grand Company requests, leves, or eventually beasttribe quests.

Pre-50 for your combat classes, you should be able to make do with dungeon drops and quest rewards, and spend Grand Company (GC) seals on any improvements. Especially try to keep your weapon up-to-date; you'll have a much easier time holding aggro.
As you outgrow GC stuff, just trade them back in for seals if you need space. You can always buy them back much more easily later.

Once you're 50.. I recommend doing quests and FATEs until you're 51, and buy new gear from NPCs in Ishgard. Even though it's mediocre "white" gear, it's vastly better than any of the free stuff you'd have at Lv.50.
Once you outgrow those, you can convert it if it's fully spiritbonded, or sell it back to an NPC.