It's perfectly possible to run through the game with the LBX the game gives you. Armor of the same type (Knight, Brawler, Tank, etc) have the same defense and weight overall; The only differences between armor is weaknesses and resistences. That'll be important late post-game, but you don't need to worry now. If you're having trouble, here's my tip: Dual-wield single-shot pistols. They're OP.