The manual does touch on center of gravity, basically just stating that it is prebalanced and unless you change something there is no need for balancing.
No mention anywhere about adding more RB's to hold it down though. Did not think 2 was enough.

The battery came installed and seems secure. Should I take it out and make sure it is wrapped?

Also the antenna goes out the back of the tail of the plane. Should I secure the end so it is not loose?