Question about Tactic's Ogre: Let us Cling Together (PSP)?

I am currently in Chapter 4 of the game but I recently realized that I've missed out on recruiting certain characters in the game and I'm wondering if it's possible to revisit previous chapters at this point in the game? Alternatively, when I beat the game, is there a way I could go back to chapter 1 in order to level the characters and/or classes that I haven't experimented with? Thanks in advance for your response(s)!