I would suggest two things since this discussion is not specifically a product support issue. The changes for what you want to do are going to require alot of your time. I suggest if you need further guidance you can post in our mod forum. Now you need to compare many templates to do something like this like showproduct1,editproduct1,uploadproduc1,showcat1 templates to the original templates to see the changes that need to be made. This is not an easy task to say the least. For example the change I gave you above will allow you to upload images but you will not be able to see them. Hense you need to compare showproduct and showproduct1 templates and see what to ad.
If you want to compare files I suggest you use a program called beyond compare by http://www.scootersoftware.com
. You can compare each file between forsale and wanted to see the difference.
Here is also a link on how to create additional template sets FAQ--How to Create Additional Template Set's in Classifieds