Hi masher - well done on the pre-op weight loss. There is absolutely no reason why this should not continue for the first 4-6 weeks post-op whilst you are on liquids. During this liquid stage, the volume is more important than the total calories.
Once you move onto purees, then soft then hard/crunchy foods then you need to be thinking more about calorific intake.
Until my first fill, as I had no restriction, I kept to my WW points and lost an average 2lbs per week.
Good luck. The pain won't last long.