You should use a tweening addon (like LiteTween) or manually using lerp and other actions to move the orb between the enemy and the player. Tweening looks better since you can use different curves for the movement acceleration and deceleration.
For the number of orbs per enemy, that could be implemented by a simple integer variable "orbCount". When the enemy dies, loop "orbCount" times and spawn an orb in every iteration.
To better organize your game, there should be a distinction between destroying an enemy (the object) and killing an enemy (its hp goes to zero). Sometimes, at the end of the level, you want to destroy all enemies but don't want to "kill" them (e.g you don't want the score to increase after a game over, you don't want them to drop more loot, etc). I'm solving this with my Health addon, check it out.