I had spent 20k on armor and then when I gained 3 more levels I bought another 10k worth of armor..
Oh god, stop that.
While you're leveling, you'll get plenty of gear from quests and dungeons. I would only consider buying gear if you've got a gaping hole in your equipment somewhere.
Spiritbinding is for making materia. Once something is 100% spiritbound (and you've completed the necessary quest), you can convert that gear into materia which can be melded into other gear either by you or by a crafter with the appropriate level.