When I'm done with the meal plan.... How do I maintain successfully?

Hi all! I'm ending week two and lost 4.5 pounds and more importantly I feel better than I have in the last ten years. I'm a little worried though. What do I do when it's done and I want to maintain? I don't want to put weight back on. I will continue clean eating but... I'm not sure how to shift portion sizes to Maintenance mode rather than weight loss without spending the rest of my life using measuring cups for chopped peppers. Any advice would be appreciated! Happy sweating!