Finding the Sum of Values of Multiple GameObjects in an Array + Variable Sized arrays

So I'm currently doing a Blackjack game and my original intent was to make each card it's own separate object which would only be rendered once the player clicked hit. I want to make it slightly more sophisticated, so I've created a new GameObject/Script called BoxController.

What I want to do is, in BoxController, have an array with the card GameObjects (which attached to them is a script containing the variable I want to access (The card number).

Once I access this variable, I then want to figure out the total amount of

My Current Relevant Script is here:

BoxController (Script 1):

 {
     //This is the array that contains the card gameobjects which in turn have the script attached.
     public gameObject[] cardsInBox;
     float boxTotal = 0;
     for (int i = 0; i < cardsInBox[].Length; i++)
     {
         //This is the line I'm very unsure about, I want to grab the variables from Cards, and then add them all together to form boxTotal.
         boxTotal += cardsInBox[i].cardNumber about;
     }
     return boxTotal;
 }

Cards (Script 2):

 //This is what I'm trying to access, there will be multiple gameObjects containing these.
 
 public int cardNumber = 1;
 
 public int suitTexture = 0; 
 
 //The card number is changed when Instantiated.

 void Randomizer()

 {
     //If the space bar is hit, randomize card values and suit values
     if (Input.GetKeyDown(KeyCode.Space))
     {
     cardNumber = (int)Random.Range (1,13);
     suitNumber = (int)Random.Range (0,4);
     }
 }

Also, I want to be able to instantiate and add a new card into cardsInBox[] every time the "Hit" button is clicked, I'm assuming it would go something like this:

 for (int j = 0; j < cardCount, j++)
         {
             for (int i = 0; i < cardCount, i++)
             {
             //instantiate a card, with vector 3 x and z being incremented by j(This way the cards keep moving and don't 
             }
         }
         if (Input.GetKeyDown(Keycode.H))
         {
             cardCount++;
         }

I haven't tried it in unity yet as I'm very unsure whether I can change the size in an array using this method.

If anything is unclear please let me know and I'll clarify.