You can mostly be self sufficient. When you get to higher level crafting (really anything post 50) a lot of the more expensive materials for combat gear will come form combat activities. Basically the crafting materials that you can buy with GC seals, find in dungeons, or buy with soldiery tomes, although you can get lots of GC seals form crafting and gathering as well. You can also buy several materials with Ixali oaknots.

I suppose it's not so much that you can't be self sufficient, but past 50 the more difficult/ expensive materials can't be gathered.