The O+ materials are in chests (all of this info is on the frontsite), and as previously stated, you need to cut the costs in half with an Energy Crystal.

Love your Lock-On button. It'll identify where he is very quickly and most of the time turn the screen to face him. If you somehow get knocked into the air, then use Retaliating Slash (square) liberally. Since you're such a low level, Berserk Charge will be another one of those abilities you'll definitely want equipped, along with Horizontal Slash.