Will 0.5 ml of dermal filler be enough to make a difference in my lips? Or would a full syringe be better?

This will depend on the final results you want. You would get a nice improvement with lip fillers (Volbella, Restylane, Juvederm). Most Doctor's start with one syringe. Nova threads can be used to improve lift and shape. Implants or fat are alternatives. I recommend getting a formal evaluation with a facial sculpting expert to go over your desired results. Best, Dr. Emer

This will depend on your goals and which filler is used. You already have nice volume and shape with your lips. Make sure you see an experienced physician provider for an in-person consultation and evaluation. Best wishes.