You can have random 'reload' and firing times by doing this:
Add the Timer behavior to your villains (enemies)
On start of Layout:
---> Enemy: Start Timer "fire" for random(1,3) (regular)
On Timer "fire":
---> System: Create object "bullet" on layer 0 at (enemy.X, enemy.Y)
This will make them shoot a bullet every 1 to 3 seconds.
I hope this helps!