Magento – Product Count Per Category in Magento

You can use robots.txt to do so. To stop certain category to be indexed by search engine you can use below code in your robots.txt file

User-agent: *
Disallow: http://mysite.com/category_2/sub-category_2.html

You can add the links of whichever category you want in similar fashion. Hope you are clear on this.

To learn more about robots.txt you can refer some links robots.txt, robots.txt tutorial, robots.txt in Magento

To add robots.txt you just need to create a file named robots.txt and upload it on the root of the folder so it is accessible like www.mysite.com/robots.txt

After that you can write the above code in that file and upload it in your root folder

Yes, use this code

$products = Mage::getModel('catalog/product')->getCollection()->addAttributeToFilter('visibility', 4);

It will get you the visible products, since 4 means Catalog and search visibility. You can combine that with this to add stock check

Mage::getSingleton('cataloginventory/stock')->addInStockFilterToCollection($products);