commerce kickstart checkout product items validation alteration module

Custom module .info file code:
name = Custom Module
description = "Provides a various customizations"
package = Custom
core = 7.x
version = "7.x-2.0"

Custom module .module file code:

function custom_form_alter(&$form, &$form_state, $form_id){
 	if($form_id == 'views_form_commerce_cart_form_custom_default'){
		if(isset($form['actions'])){
			$action_submit = $form['actions']['checkout']['#submit'];
			$form['actions']['checkout']['#submit'][0]='custom_cart_checkout_form_submit';
			foreach($action_submit as $key => $callback){
				$form['actions']['checkout']['#submit'][] = $callback;
			}
		}				
	}
	
	if($form_id == 'webform_client_form_77') {
		$form['submitted']['enter_your_account_name']['#attributes']['placeholder'] = "ENTER YOUR ACCOUNT NAME";
		$form['submitted']['enter_']['#attributes']['placeholder'] = "ENTER YOUR P.O NUMBER";
		$form['submitted']['adrress_line_1']['#attributes']['placeholder'] = "ADDRESS LINE 1";
		$form['submitted']['adrress_line_2']['#attributes']['placeholder'] = "ADDRESS LINE 2";
		$form['submitted']['city']['#attributes']['placeholder'] = "CITY";
		$form['submitted']['county']['#attributes']['placeholder'] = "COUNTY";
		$form['submitted']['postcode']['#attributes']['placeholder'] = "POSTCODE";
	}
	
	if($form_id == 'webform_client_form_97') {
		$form['submitted']['first_name']['#attributes']['placeholder'] = "FIRST NAME";
		$form['submitted']['surname']['#attributes']['placeholder'] = "SURNAME";
		$form['submitted']['company_name']['#attributes']['placeholder'] = "COMPANY NAME";
		$form['submitted']['email_address']['#attributes']['placeholder'] = "EMAIL ADDRESS";
		$form['submitted']['phone_number']['#attributes']['placeholder'] = "PHONE NUMBER";
		//print_r($form['submitted']['postcode']);
		$form['submitted']['postcode']['#attributes']['placeholder'] = "POSTCODE";
	}
}

function views_form_commerce_cart_form_custom_validate($form, &$form_state){
 
}


function custom_cart_checkout_form_submit($form, &$form_state) {
	$view = $form_state['build_info']['args'][0];
	
	$submitted_values = $form_state['values']['edit_quantity'];
	
	$cart_product_types = array();
	$type = "";
	$default_qty = 0;
	
	foreach($view->result as $key => $result){
	//print_r($result);
		$type = $result->commerce_product_field_data_commerce_product_type;
		$qty = $result->commerce_line_item_field_data_commerce_line_items_quantity;
		
		if(isset($cart_product_types[$type]['total_qty'])){			
			$cart_product_types[$type]['total_qty'] += 	$submitted_values[$key];
		}else{
			$cart_product_types[$type]['total_qty'] = $submitted_values[$key]; 	
		}
	}
	
	$packeage_limit = array('bundle1' => 24, 'bundle2' => 12);
	$error = false;
	$case_type = 'case';
	foreach($cart_product_types as $type => $group_item){		
		if($group_item['total_qty'] % $packeage_limit[$type] != 0 && $type != $case_type){
			 drupal_set_message(t('It should be multiple of '.$packeage_limit[$type].' for '.$type.' to add to the cart.'),'error');
			 $error = true;
		}
	}
	
	if($error){
		drupal_goto("cart");
	}
}