Personally, I'd go with fat, anytime. Sugar will give me cravings, which will lead me to eat far more fat over the next three days than the one serving of ranch. Flour will do the same, if it's "enriched" or white flour. Fat I can handle by mitigating my intake the rest of the day. So I'd have steamed broccoli with fresh lemon juice instead of cheese sauce or SmartBalance later that day, etc. Does that make sense?
I know the feeling...those kind of choices hit me daily, too!
Regarding calories, there isn't a specific calorie requirement for SBD that I know of. You definitely do want to stick to serving sizes of most items and keep your calorie intake moderate, but as you work with the plan, you'll figure what you can eat and still lose weight. Servings of nuts and dairy are limited, so that helps reduce your calorie intake, as does the 75 cal per day limit to sweet treats.
You may want to put your daily choices into
www.fitday.com in order to figure out how many calories you are consuming.