Upgrade, Migrate, and Improve Magento Store

We have a running Magento site version 1.6.2 and need to upgrade to 1.8.1. At the same time migrate existing design template to a newer version. Customize the new template based on look & feel of current site and to accommodate the new magento platform. Upgrade all extensions to newest versions if available and enable their compatibility to the new magento platform and to the new design template. Existing magento, design template, and some extensions were modified, need to migrate these modifications too. Improve on a few items - loading speed and functionalities etc. Please refer to the requirements attached. We look for freelancers with lots of magento experiences, but most important of all, excellent completion rate and good service record.