Sam,
First off congratulations on making the decision to improve your health. My journey has been different from most on here, but my starting BMI was similar to yours so maybe your results will be similar to mine. I was 325 lbs at 5'7". I did not have to follow the strict pre and post-op diets. I was asked to lose 10 lbs before surgery, but it wasn't required. I lost 8lbs and the surgeon still did the surgery. The first day after surgery I was on a clear liquid diet followed by a week of full liquids. After my post op visit with the surgeon I was cleared to resume a normal diet. It was slow going the first couple of weeks. I ate a lot of fat-free refried beans and ground meats. Just remember to chew very well and eat slow. My surgery was on March 16, 2012 and I am down 70lbs so far. I follow a pretty stict mealplan with no white grains of any kind. I eat only lean meats, veggies, fruits and whole grains. But I do allow for treats now and then. I keep Skinny cow or Weightwatchers ice cream bars that are 100 calories or less per serving on hand in case I have a sweets craving. For exercise I mainly walk or do yardwork, but I bought a beginner Kettlebell exercise video that I have done several times and really like that too.
My biggest advice for you as you prepare for surgery is to get your head in the game. Start practicing your new eating habits. Eat slow, small bites. No drinking while eating or for 1 hour after. Cut out the things that you most likely won't be able to have after surgery. I was a huge bread and diet coke junkie before surgery. I cut them out 2 months pre-op and now I don't crave them. Good luck to you. You will do great if you stick with it!