How to change scripts to include Waves of Enemy?

Spawn script, 2nd script is Score managing script.

 var spawnPoints : Transform[];  // Array of spawn points to be used.
 var enemyPrefabs : GameObject[]; // Array of different Enemies that are used.
 var amountEnemies = 1000;  // Total number of enemies to spawn.
 var yieldTimeMin = 2;  // Minimum amount of time before spawning enemies randomly.
 var yieldTimeMax = 5;  // Don't exceed this amount of time between spawning enemies randomly.
 
 function Start(){
     Spawn();
 }
 
 function Spawn(){ 
    for (i=0; i<amountEnemies; i++){ // How many enemies to instantiate total
       yield WaitForSeconds(Random.Range(yieldTimeMin, yieldTimeMax));  // How long to wait before another enemy is instantiated.
 
       var obj : GameObject = enemyPrefabs[Random.Range(0, enemyPrefabs.length)]; // Randomize the different enemies to instantiate.
       var pos: Transform = spawnPoints[Random.Range(0, spawnPoints.length)];  // Randomize the spawnPoints to instantiate enemy at next.
 
       Instantiate(obj, pos.position, pos.rotation); 
     } 
 }  


     @script ExecuteInEditMode()
     
     var currentScore : int = 0;
     
     var time : float = 0.0;
     var hitCrosshairTexture : Texture;
     private var alphaHit : float;
     var hitSound : AudioClip;
     
     var mySkin : GUISkin;
     
     var pointsToNextRank : int = 50;
     var rank : int = 0;
     var rankSound : AudioClip;
 
 function Update () {
 
     if (time > 0){ 
         time -= Time.deltaTime;
     }
     alphaHit = time;
 }
 
 function DrawCrosshair(){
     yield WaitForSeconds(0.1);
     time = 1.0;
     audio.PlayOneShot(hitSound, .5);
 }
 
 function addScore(value : int){
     yield WaitForSeconds(0.2);
     currentScore += value;
     
     if(currentScore >= pointsToNextRank){
         rank++;
         PlayAudioClip(rankSound, transform.position, 1.0);    
         pointsToNextRank += currentScore;
     }
 }
 
 function PlayAudioClip (clip : AudioClip, position : Vector3, volume : float) {
     var go = new GameObject ("One shot audio");
     go.transform.position = position;
     var source : AudioSource = go.AddComponent (AudioSource);
     source.clip = clip;
     source.volume = volume;
     source.pitch = Random.Range(0.95,1.05);
     source.Play ();
     Destroy (go, clip.length);
     return source;
 }    
 
 function OnGUI(){
     GUI.skin = mySkin;
     var style1 = mySkin.customStyles[0];
     
     GUI.Label (Rect(40, Screen.height - 80,100,60)," SCORE :");
     GUI.Label (Rect(100, Screen.height - 80,160,60),"" + currentScore, style1);
     
     GUI.Label (Rect(40, Screen.height - 110,100,60)," LVL :");
     GUI.Label (Rect(100, Screen.height - 110,160,60),"" + rank, style1);
     
     GUI.color = Color(1.0, 1.0, 1.0, alphaHit);
     GUI.DrawTexture (Rect ((Screen.width - hitCrosshairTexture.width)/2, (Screen.height - hitCrosshairTexture.height)/2, hitCrosshairTexture.width, hitCrosshairTexture.height), hitCrosshairTexture);
 }