Do I need at metal prop if I am going to run two 3S 11.1v 5,000 Mah LiPo's?
If you want that's fine, you can run the stock plastic prop. be sure to bring along some spare around 5pcs. to enjoy the boating. Plastic props are known for some flex issue and this will apply on a WOT with the 3s Lipo power, that's why a lot of us use the metal props.
Sharing is the best thing to do on EARTH legally.
I have had the stock plastic props break using 3s lipos.