It shouldn't really be necessary to "start again", you look to have setup lots of mappings etc so it would be painful to do that. Just FYI to do that the easiest way is to just delete or rename the Goodreads Sync.json file from your plugins folder.
You didn't say the datatype of your custom column etc. What I suggest you do is try the exact example that I described above in post #49. Create a fake book if you want to, link it to Goodreads, start with one simple tag on it as per that Science Fiction example and follow the steps exactly. If you can get that to work then you can experiment a bit more and see if you can figure out why others are not working. If you still can't get anywhere send me a PM with your email and I will send you a special debug build that will print some output to give the details.