I had the duodenal switch and our diet was regular foods, but mostly protein, and smaller portions. It was an individual process, in that what worked well for one person didn't for another. Also, if something didn't work well, we tried it again a week or two later, and often were fine.
About the psych eval, I think they really want to know that you have an understanding of the procedure, you understand the risks, are reasonable in your expectations and that you understand and will adhere to the lifestyle changes necessary for success and health. I don't think they want to delve into your murky past so much as to make sure you are dealing in reality in the present, honest! I did go to a psych associated with my weight loss surgeon, but wonder if you couldn't find a WLS-knowledgeable psych near you.
I am just starting school, for a degree in human services, and in about 92 years should have a degree in social work, and hope to counsel WLS patients, so if you want to wait that long, I'll do it!
Take care,
Dawna