Magento Site Cleanup

We have an ecommerce site built in Magento 1.4.2. We have several issues that we would like addressed with the site: 1. The site has failed WC3 validation and we'd like to get the 34 errors fixed. 2. We also have an ongoing PHP Fatal error showing up in the server error log: PHP Fatal error: Undefined class constant 'VAR_DIRECTORY' in /.../[login to view URL] on line 63 It does not seem to effect site performance, but we'd like to get it cleaned up. 3. We had started to upgrade to Magento 1.6 several months ago, but decided to hold off. There are now quite a few unused files and directories related to the upgrade that we would like to have cleaned up. We would like to get the site cleaned up with minimal downtime. When yo place your bid please let me the following: 1. When you can start 2. How long (if at all) you expect the site to be down 3. How long to complete the project 4. Any other information you will need Thank you.