Create an array of sprites and create them at start.

Hi all! I'm here to ask you how you would achive this thing i want to do. I'm experimenting with the new features of Unity4.3. What i want to do is to take all letters i've inside a folder and create fromt these a keyboard placing them dinamically on the screen. What i did since now is this:

 using UnityEngine;
 using System.Collections;
 
 public class Letters : MonoBehaviour {
 
     private char[] keyboard = new char[] {
         'a',
         'b',
         'c',
         'd',
         'e',
         'f',
         'g',
         'h',
         'i',
         'j',
         'k',
         'l',
         'm',
         'n',
         'o',
         'p',
         'q',
         'r',
         's',
         't',
         'u',
         'v',
         'w',
         'x',
         'y',
         'z'
     };
     float posX = -4.5F;
     float posY = -0.65F;
 
     
     // Use this for initialization
     IEnumerator Start () {
         for(int i = 0; i <= keyboard.Length; i++){
             posX = posX + 0.65F;
 
             if(posX > 3.5F){
                 posY = -1.5F;
                 posX = -4.15F;
             }
 
             string path = "file://"+Application.dataPath+"/Tastiera/"+keyboard[i]+".jpg";
             SpriteRenderer renderer = gameObject.GetComponent<SpriteRenderer>();
             Sprite sprite = new Sprite();
             WWW www = new WWW(path);
             yield return www;
             sprite = Sprite.Create(www.texture, new Rect(0, 0, 0, 50),new Vector2(posX, posY),100.0f);
             renderer.sprite = sprite;
         }    
     }
     
     // Update is called once per frame
     void Update () {}
     }

Ofc, it doesn't work, what it do is creating every time a sprite replacing the one it created before. What i tought to solve this was: At start i fill an array with sprites then i iterate on this array and create N istance of these letters.

How can i should do that? thanks a lot.