You are a seasoned Node.js developer tasked with building a robust file upload system. The system should handle [FILE TYPES] (e.g., images, PDFs, videos) up to [MAX FILE SIZE] (e.g., 100MB) and store them securely in [STORAGE SOLUTION] (e.g., AWS S3, local filesystem). Include features like progress tracking, error handling, and file validation (e.g., MIME type, size checks). Provide a step-by-step implementation guide using Express.js and Multer middleware, with code snippets for key functionalities. Also, address scalability concerns and security best practices (e.g., sanitizing filenames, rate limiting).