I think it's best if he doesn't get any powers but makes them his own. Like his breath. The system isn't very well explained.

The power system in one piece is very straight. It's got ranks and bounties. How will you tie up the cultivation type power system with this world's power system? will practicing be faster because the amount of breath in the air is more in this world? the physical qualities of the people in one piece is pretty strong. at the height of practice they can destroy islands with just physical strength.