Magento – Is it possible to display the gross profit of a product as an attribute in the admin page of a product

Creating a new product will not generate product->id that you are passing in updateStock Method so that is why updateStock is working only for existing products.

I would suggest to check

$product = Mage::getModel('catalog/product');
    $product->load(18); //18 is my existing product id
    echo '<pre>';
    print_r($product->getData());
    exit;

This will give you idea about data associated to product.

Recently, I have created a method that is used to create product. Please review it.

public function createProduct($categories = array(3),$productName,$sku,$price=0,$productDescription,$productShortDescription,$status,$visibility,$attributeSet,$taxClass,$qty,$stock,$websites = array(1),$productImage='',$productMetaTitle,$productMetaKeyword,$productMetaDescription) {             

    $product = new Mage_Catalog_Model_Product();        
    // Build the product
    $prod = array(); 
    $prod['sku'] = $sku;
    $prod['attribute_set_id'] = $attributeSet;
    $prod['type_id'] = 'simple';
    $prod['category_ids'] = $categories;
    $prod['website_ids'] = $websites;
    $prod['name'] = $productName;
    $prod['description'] = $productDescription;
    $prod['short_description'] = $productShortDescription;
    $prod['weight'] = '1';
    $prod['status'] = $status;
    $prod['url_key'] = Mage::getModel('catalog/product_url')->formatUrlKey($productName);
    $prod['url_path'] = Mage::getModel('catalog/product_url')->formatUrlKey($productName); //TO-DO :: find correct method
    $prod['visibility'] = $visibility;
    $prod['price'] = $price;
    $prod['tax_class_id'] = $taxClass;
    $prod['meta_title'] = $productMetaTitle;
    $prod['meta_keyword'] = $productMetaKeyword;
    $prod['meta_description'] = $productMetaDescription;
    $product->setData($prod);
    $product->setStockData(array( 
        'is_in_stock' => $stock, 
        'qty' => $qty,
                'manage_stock' => 1
    ));
    if($productImage) {
        Mage::app()->getStore()->setId(Mage_Core_Model_App::ADMIN_STORE_ID);
        $product->setMediaGallery (array('images'=>array (), 'values'=>array ()));
        $product->addImageToMediaGallery($productImage,array('image','small_image','thumbnail'),false,false);
    }
    try {
        $product->save();           
        return $product->getId();
    }
    catch (Exception $e){
        echo $e->getMessage();
    }               
}

Hope above method helps you.

Also if you set manage stock from System->Configuration->Catalog->Inventory->Product Stock Options to Yes, then you don't need to pass manage_stock in above method. Product will be automatically created with manage stock set to yes.

you need to add this in your config.xml under the config tag.

<adminhtml>
    <layout>
        <updates>
            <tbe_report>
                <file>tbe_report.xml</file>
            </tbe_report>
        </updates>
    </layout>
</adminhtml>

then create the file app/design/adminhtml/default/default/layout/tbe_report.xml and put your layout updates in there.

[EDIT]
your layout handle is determined from the url of the page.
Just replace admin with adminhtml and replace the slashes with underscores.
If the action is index and is not present in the url just add it in the layout handle.
Here are some examples to make it clearer.
If the url is admin/tbe_report/something then the layout handle is adminhtml_tb_report_something.
if the url is admin/tbe_report/ then the layout handle is adminhtml_tb_report_index.