I just finished Chapter 4, was very hard. You can try an easier chapter and level up, as long as you finish that chapter will save all exp and materia earned and can go back to another chapter.
Gotta say its a lot of fun, you really need to have a game plan and not go in guns blazzin, I recommend using barrier spells, the Iron Maiden bracelet, and the Steadfast block materia.
Provoke+lifesaver ability+Autocure with barret has made hard mode much more manageable for me. He tanks a lionshare of the damage while the others do their thing.