Can this spell be cast multiple times (round after round) by the same caster?
If so, does each weapon require a move action to move?
Yes. Yes.
Well, the spell says that once the weapon has a target, it will continue to follow that target until it is killed or until you use a move action to direct it elsewhere. Once its target is dead, it takes a move action to designate a new target. So, you can have a cloud of spiritual weapons attacking a single target and, should that target move, the cloud of weapons will follow it. Once that target dies, you will need to use a move action for each weapon to assign them a new target.