Full-Stack Developer for AI-Powered MVP — Complete & Launch Existing Platform (NOT a Rebuild)

I am looking for an experienced full-stack developer to take over, complete, and launch an existing AI-powered MVP. Important: Existing Product — Not a Build-from-Scratch Project The platform is already substantially developed and includes working product functionality. I need a developer who can evaluate the existing codebase, preserve and improve working functionality where appropriate, complete the remaining production work, and prepare the application for launch on our existing infrastructure. The goal is to make practical use of the existing work and avoid major changes unless there is a clear technical reason to make them. Existing Product The application currently includes: * AI-powered core workflow (input → AI processing → output) * User onboarding and account flow * Project/data structure associated with individual users * Credits or usage-based logic * Admin and billing UI structure * API integration layer connecting to the AI platform * Initial deployment on Vercel The existing codebase and repositories will be available for review. Current Technology * Next.js * NestJS * AI/LLM platform integration * SaaS subscription and usage model * Vercel I am open to reasonable architectural recommendations where they improve reliability, security, maintainability, or scalability. Any significant architectural change should be supported by a clear technical justification and discussed before implementation. What I Need 1. Existing-Code Technical Audit Review the current application and identify: * What is working correctly * What can be reused as-is * What requires minor fixes or improvements * What may require restructuring or replacement * What remains incomplete for production launch * Any technical risks or dependencies that should be addressed The goal is to establish a practical completion plan before moving into additional development work. 2. AI Integration Preserve and complete the existing AI workflow, including: * Reliable AI/LLM API integration * Usage and cost tracking * Rate limiting * Error and failure handling * Appropriate handling of unsuccessful or incomplete AI requests 3. Accounts & Core User Flow Complete and verify the production-ready account and authorization flow so users can securely access only their own data. The core experience should allow users to: * Create and manage projects * Run the core AI workflow * View generated results * Track usage/credits * Manage their subscription and billing information Where the existing UX is functional, the preference is to improve and extend it rather than unnecessarily replace it. 4. Billing & Usage Complete and verify: * Subscription handling * Plan configuration * Usage limits * Credit/usage enforcement * Relevant billing-related workflows 5. Production Launch Prepare the application for launch, including: * Vercel deployment * Production environment configuration * Error handling * Basic security review * Production readiness checks * Basic monitoring and logging Development Approach The existing codebase should be treated as the starting point for the project. I am looking for a developer who can make a technical assessment before recommending substantial changes. If a component genuinely needs to be replaced or substantially reworked, please explain: * What currently exists * The technical issue or limitation * Why the existing implementation is not suitable * The proposed approach * Estimated effort * Expected benefit The objective is to make the application production-ready efficiently while maintaining code and functionality that are already working well. First Milestone — Paid Technical Audit The first milestone will be a paid technical audit of the existing repositories and application. The deliverable should be a concise completion report covering: Existing feature → Current condition → Recommended action → Technical reason → Estimated effort This assessment will be used to determine and prioritize the next development milestones. Please base your estimates on the existing codebase rather than treating this as a new application build. When Applying Please include: * Examples of SaaS products you have built, completed, or migrated * Your experience with Next.js * Your experience with NestJS and backend APIs * Your experience integrating AI/LLM platforms * Your experience deploying applications on Vercel * A brief explanation of how you evaluate an existing codebase before deciding whether to reuse, refactor, or replace a component Most importantly: If an existing MVP already has working logic, UI, and core workflows, how do you determine what should be reused versus refactored or rewritten during the completion phase? I value a practical, engineering-focused approach that builds on existing work where it is technically sound while making necessary improvements for production readiness. This may develop into an ongoing engagement for the right developer after the initial launch.