Convert existing website to Wordpress with Shopp shopping cart plugin

Current existing website [login to view URL] needs to be converted to a Wordpress custom theme with the Shopp shopping cart plugin. Willing to consider other CMS if you can find a equivalently powerful shopping cart that will integrate with our existing web design. Shopp is currently the only shopping cart that we're aware of that supports the options and configurations that our site will require. Lots of products can have 20+ configurations when they're being configured and this is the only cart we've found that handles this. For instance selecting the amount of RAM, size of SSD, installation of OS, type of touchscreen, paint color from standard pallet, etc. all need to be configured by radio buttons and check boxes on the product page before being added to cart. We tried Drupal and Shopify in the past, neither had the levels of configuration we need for a computer system design/build website. We like our layout and design, no changes will be made to anything visual other than adding "add to cart" "view cart" etc. kind of things. Shopping cart with multiple levels of customization of products on the product page. Website needs ability to have accounts creatable and customers can log in and pay invoices via CC or paypal. Accounts should also have the ability to view areas of the website the public cannot. URL masking is a must, 404 redirects, etc are probably all features in Wordpress. Possible integration with Google Shopping and Amazon a huge plus. Obviously our current design will need to have CSS adjusted and lots of other tweaks, I can handle most of this as I designed and coded the website from scratch including all pictures and artwork. I understand the time it takes to make a website and the time it takes to learn the skills to do it well. I overall really like how our layout and navigation flows, I do not want to change the UI. Let me know what you think, I'll work with you in whatever way you need. [login to view URL]