Generally a good rule of thumb is to check out shops every time the story advances. Usually the stores get equipment that's one notch better.

Some bosses require strategy to beat, but even the hardest ones can be defeated by an overleveled party. I generally spend time in random battles until the current armor becomes ineffective.

This game is super cutomizable, so you can alter your party's composition and skillsets until they can be anything you want them to be. Kind of like in FFI, but you can change your mind later.

Getting through the game is mildly difficult, but getting all the sidequests and rare items requires a lot of time and patience. This is the only game I've ever completed everything.

The game has several exploitable glitches that will make your life easier. I suggest that you wait until the second playthrough before exploring these.