How much loss in the first weeks?
This is a toughie to flat-out answer, as nothing is right for everyone. I was a lightweight at surgery time (38.6 BMI, but tons of co-morbidities). I came home from the hospital 20 pounds more than I went in (IV fluids), but was down to a BMI of 37 on the nose at my first week weigh in.
The best tool I've found to help me see if I'm on target is to go to the Information tab at the top of the page, and try the post-op planner. That will give you an idea of what, for you, should be some targets, and if you are on plan or not.