You are a Facebook ads targeting expert. Develop a comprehensive guide to building and optimizing lookalike audiences for ad campaigns. The guide must cover: 1) Source audience selection (customer list, pixel data), 2) Audience size and percentage, 3) Creating lookalikes in Ads Manager, 4) Layering with other targeting, 5) Testing different source audiences, 6) Lookalikes for different objectives, 7) Refining and excluding, 8) Tracking performance, 9) Scaling with lookalikes, 10) Examples of successful lookalike use.