magento site redesign

I currently have two websites with a proprietary backend admin system that are actively selling products. One of these sites is a simple single product sales page, the other is our core website with all products and both use the same limited backend system. I have contracted the creation of a new core website using the ecommerce platform Magento (version 1.2.1.2) which mimics the design of the current core/multiproduct website. The site that was created is not easily upgradable to newer versions of the ecommerce platform because it was not designed as a theme, and directly uses some modified core modules of Magento. What I need help with: 1. redesign the magento core site so that it uses a theme/template with our design and upgrade it to magento version 1.4. There is potentially some flexibilty here to use an existing magento template, but it is important that automatic upgrades are possible without having to totally rework magento core files every time. At the same time the design of the magento site should be upgraded. I want to maintain a clean professional look which is easy to navigate and seo friendly. Our products are of medical/dental nature so the design should resemble other medical/dental sites. 2. Add in multiple stores Magento offers the capability of linking additional single-product websites to use the checkout capabilities. I need to add in a number of additional stores/websites with new products. I will create the single-page websites on another host so the task consists of designing a template for use outside and inside the magento store and hooking up the outside webpage to Magento. I currently have three websites in preparation for this purpose. 3. Perform some seo work on the single page sites and magento 4. setup split testing to optimize adwords campaigns There are a variety of other tasks that I am looking to achieve in the near future which are both design and marketing oriented, so I am looking for a partner that I can work with for an extended period of time.