Male sheep are rams, and they don't lead the flock. Usually, the oldest female, or ewe, does.
Bellwether
Both terms are correct.A "shepherd" is one who herds sheep, rather than a "flocker."
A male sheep is called a ram and a desexed male sheep is called a wether.
A ram or wether (if it has been castrated).
A flock, a herd or a mob.