Welcome and I will try to answer your questions in the order you have asked them in, but my answers are only from my experience and perspective : -
The options between a Band / sleeve / bypass can be made depending on your BMI. If your BMI is in the higher range then you may be probably recommended a sleeve or a bypass. Also there are higher long term success rates with a sleeve, and higher still with a bypass. I chose to go with a sleeve rather than a bypass though as there were other side effects of a bypass that I wanted to avoid such as malabsorption.
The pre-op diet depends on what your surgeon wants, my surgeons recommended a diet, but not the milk diet, I had slim fast twice a day and a light meal in the evening.
I had wind pain after the surgery but no other real pain, it was just a bit difficult getting up and down from the bed for the first couple of days. I was also quite careful not to put any tension on my wounds, (i.e. not reaching things out of tall cupboards) for a few weeks post-op.
The post-op diet is as recommended by your doctor, I think I was on fluids for a week, then very puree for two weeks, then soft diet for two weeks. I am two months post op and can eat any texture food, however some things are tolerated better than others.
I had half a glass of white wine on Saturday night, first alcohol since surgery and was fine. The advice I got was to wait until after my first out patients, which I had last week.
Hope the above helps?