How Many Dress Sizes Will I Lose After Smart Lipo?

It's really hard to answer your question without seeing you or knowing how much fat you have that can be removed. Liposuction is not to make you a certain dress size or make you lose weight, it's to get rid of isolated pockets of fat.

Smart Lipo is a great tool, but it isn't something that can definitively deliver dress size changes. For example, sometimes we don't even see a dress size change depending on the area that we do. On the other hand, it can change shape and that can be just as important!
As far as needles go, you will have needles whether you go with the regular method of liposuction, SmartLipo or tumescent. In SmartLipo, there will be many needles, but they aren't all that painful if done right.
Lastly, about weight, you didn't ask, but to let you know - you won't lose any pounds in this procedure or if you do, it will be only about a pound or so. This is solely about size and shape. If you have that much weight to lose, it might not help you to get it done without significant work on diet and exercise, but go see an *ethical* cosmetic surgeon in your area and hopefully they will be honest with you. Good luck!