Custom wordpress plugin using XML

I need a wordpress plugin made. It's meant to automate updating my wordpress blog's content with information from an XML file. My shopping website (not my blog) automatically creates an XML file (GZ) which includes all of my products, pricing, descriptions, images, and more information. I want this plugin to automate the process of: pulling XML file, comparing my blog content with XML content, and update all information. When your plugin is complete, it will create/remove any categories my products belong to, add all new products, hide any products not in stock, and update my wordpress with this data. Since my site offers 455,000 SKUs and growing, it's very important to have a very smart comparison in order not to bog down the server. The purpose of my blog is to inform customers of products, and then they will click to order, which redirects to my shopping site. The destination link is part of the XML file. Each one of the products are to appear as posts in the blog, not pages. Admin panel should give a field asking how often to update, it should include a log so that we can figure out what is going on if we have problems, and the pictures updating should only be done if the picture changed.