Act as a seasoned startup investor with 10+ years of experience in angel networks. Provide a step-by-step guide on how to join a startup angel network, tailored for [aspiring investors] with [specific budget ranges] and [industry interests]. Include key considerations such as evaluating network credibility, minimum investment requirements, and due diligence processes. Highlight common pitfalls to avoid and best practices for building a strong portfolio. Use real-world examples where applicable.