Merge Wordpress Themes on Existing Website

I am updating my wordpress website from one custom theme to another. The existing theme is running on [login to view URL] and the new theme template has been produced in htmls/css and is being converted to a wordpress theme this week. The finished wordpress theme will be should be ready on 22nd June 2012 and delivered to the project winner. I need someone to install this new theme on my servers as soon as possible after the new custom theme is completed by the current developers. However, please be aware this is not a simple install. As well as installing the theme on the existing server and URL the following will need to be done: 1. The existing property search functionality will need to be incorporated into the new themes home page. The developers designing the new template have designed the search box only – you just need to move the search functionality to this new theme home page and use styling provided. The search function is searching an external database and not wordpress so this code needs to be kept and migrated to the new theme. a. The existing search can be see in the left hand column of [login to view URL]) b. The mapping of the old fields to new can be seen in the attached file [login to view URL] 2. Move the property search results page ([login to view URL]) into the new template. A jpg mockup can be seen in the attached property_page_final.jpg. 3. Move the property details template code into the new template (here is an existing property details page [login to view URL]) 4. Once the migration is complete All files from the old template that are no longer used (php, image, js etc) need to be removed from the server. I want the new site to run as fast as possible so don't want any unrequired files to load and slow down the process. Before any work is a done a full back up of the existing site should be done so none of these files are lost for good. The aim is to get the existing content into the new custom theme and have it loading as fast as possible. Ideally I would like all this done on a test server first before migrating to www.fasttracksales.co.uk. However, I think the property search and property details information that comes from dezrez may not work if you we use any URL other than www.fasttracksales.co.uk. Timeframe I would like the work to start as soon as possible after the template is complete (estimated to be 22nd June) and be completed very soon after that. There needs to be as little downtime as possible as the site is live and used 7 days a week. Many Thanks