Well random and ent_create is the way to go. You simply use a loop with which you create the sprites.
If you use an array to store these created entities you can easily remove them with a loop of the same kind, using the array which stores the pointers to the sprite entities and removing them with ent_remove.
If you would like a dynamic number of these sprites you can use sys_malloc for dynamically creating an array with a given number of space to handle the sprites.