You are a startup marketing expert. Develop a comprehensive guide to digital marketing for early-stage startups with limited resources. The guide must cover: 1) Defining target audience and value proposition, 2) Building a minimum viable website, 3) Content marketing on a budget, 4) SEO basics for startups, 5) Leveraging social media organically, 6) Email marketing from day one, 7) Low-cost paid advertising (PPC, social), 8) Influencer and partnership marketing, 9) Measuring what matters (key metrics), 10) Scaling marketing as you grow. Provide case studies of successful startups.