PHP code transfer work

We are upgrading ecommerce site’s script. This is purely a php programming work. We have a live site running the current (not upgraded) software. We have added quite a few customized functions and now want to transfer these codes and functions into the new files. What we want done is: 1. Move the codes in the older files into one new file for custom codes in the new system. In the previous environment, the codes are spread out in about 6 or 7 file depending on function. Now everything will be in one file to prevent overwrite in future updates. 2. Get the development site up and running and behaving exactly like the live site. All functions restored. As you know, as an experienced programmer, there may be need to sometimes modify the codes to its new environment. We don’t expect this to be much. 3. by the time all the functions are working as should, you will ensure that the code for the seo friendly URLS are working and are the same as on the live site. 4. The only new thing to be done is use an already existing code to make the products in the index page “Featured products” and “Products of the day” to behave like the product inside the site. I.e redirect to merchant shop IF only one shop. 5. When all the codes and functionalities have been restored in the development site. You will move the scripts to the live site and ensure it is running smoothly. We expect work to start ASAP. You will get access to the development site. You must be able to work all weekend. THIS IS A MUST.