I don't want you to think I have not seen this thread. However at this moment I do not have the time to go through a blank configuration and show all of the changes needed to do what you want so you don't have to use firewall rules to make a transparent proxy. The information is provided inside the configuration file, but it is all in English so I will make a basic configuration and post the file for you hopefully by the end of the weekend.
If you are afraid that you might make a mistake. The chances are high that you will never learn anything.