You have more inventory space in this game than like 10 mmorpgs combined storage space.

You don't have to buy bags and manage that
You don't have to use a cash shop to get more space.

If you have more than, what is it close to 500 items in total? Then make the effort to sell some of those things, make some gil while everyone is paying top dollar.

That or we need to get you an intervention for being a hoarder...its a disease you know....

Realistically your issue is either you took out way too many crafting and gathering classes and are trying to do it all at once, you don't know what sells and what is junk, or what is useful, and just keep it all just in case...or...you have the hoarder disease and need treatment.

How many cats do you own?