Building a fashion e-commerce marketplace starts with choosing the right tech stack, like React, Node.js, and Stripe Connect or using platforms like Sharetribe or Shopify for a faster launch. Focus on core features like seller profiles, product listings, secure checkout, and reviews. Start niche, build trust through good UX and storytelling, and grow using SEO, social media, and influencer partnerships. Automate early, keep it mobile-friendly, and scale with feedback. Launch lean, learn fast, and always keep the user at the center.