You can join a free company at any time. If you do all the side quests along side the story quests you will have quests rewards that will replace your old gear as you level. Or you can choose the cash reward and purchase crafted items from the market board.

If you wish to skip the side quests (not recommended) go to the market board every few levels to see what gear is available. As you level you will see more differentiation for tank stats. Some gear can be equipped across several classes so make sure you are purchasing gear with stats most helpful to your class. Typically items with parry would be what you are looking for.