Full-Stack Engineer(s) for a Multi-Tenant Platform: Web, Mobile, Real-Time, Payments and AI

We are building a multi-tenant SaaS platform with a mobile-first web app, an iOS mobile app, location-based features, subscription billing, a media delivery service, healthcare data integrations and an AI assistant. We have a product spec and an early prototype. We need an engineer, or a small team led by one engineer, to take it through four fixed-price milestones. We care about a working demo at each milestone, not just code we cannot evaluate. PROJECT SCOPE Milestone 1: Foundations and Architecture Review the existing prototype and codebase and give us a written assessment: what exists, what is missing, and the recommended path forward. Set up dev, staging and production on AWS (ECS, Fargate, EC2, VPC, IAM) with Pulumi for infrastructure as code. Build CI/CD with GitHub, Jenkins or GoCD, and AWS CodePipeline and CodeDeploy. Create the data layer on PostgreSQL (Aurora) and Redis, with MySQL, MongoDB and DynamoDB where each fits. Build authentication: magic-link login, JWT, API keys, role-based permissions, admin MFA and rate limiting. Milestone 2: Core Product Web app: Next.js (App Router), React, TypeScript and Tailwind CSS, plus an Angular admin dashboard. Mobile app: Flutter (Dart) or React Native for iOS, with push notifications and App Store submission. Backend services: Go 1.20+ (Gin, Gorm, goroutines, channels, gRPC) and a Node.js/NestJS API layer with Prisma. Real-time features: presence and live updates with Elixir and Phoenix channels. Location features: interactive map with Leaflet and OpenStreetMap, plus GPS proximity detection. Admin tools: a content back-office that needs no code changes. Milestone 3: Payments, Contracts and Integrations Payments: subscriptions and one-time purchases with Stripe, Paddle and PayPal behind one internal payment interface, including webhooks with signature verification, idempotency, refunds and failure handling. E-signing: Oneflow or Scrive integration for electronic contracts, with the architecture ready for BankID and ID06. Healthcare: EHR integration using FHIR and HL7 standards. Background work: message queues and asynchronous jobs. Legacy and third-party: a legacy PHP module to integrate with, plus third-party APIs. Media: a streaming service (HLS and DASH, transcoding) running on a Linux VPS. A Rust worker for the transcoding path is welcome. Milestone 4: AI, Hardening and Handover AI service in Python with FastAPI: LLM integration, RAG, and agents using LangChain, LangGraph or the OpenAI Agents SDK. Content ingestion uses Python-Goose, and early workflow prototypes may be done in Stack AI. Observability: Prometheus, Grafana and Datadog. Orchestration: Docker and Docker Compose for local and staging, Kubernetes for production (EKS on AWS, GKE and Compute Engine on GCP). Security and compliance: GDPR workflows, encryption at rest and in transit, EU hosting (AWS Stockholm), audit logs and anti-scraping controls. Testing: Jest, Playwright and Go tests on core business logic. Handover: source code in our GitHub, documentation and a walkthrough call. TECHNOLOGY REFERENCE Languages: Go, Python, JavaScript, TypeScript, Dart, Elixir, Rust, PHP. Frontend: React, Next.js, Angular, Tailwind CSS, Leaflet/OpenStreetMap. Mobile: Flutter, React Native, iOS, push notifications. Backend: Gin, Gorm, FastAPI, Node.js, NestJS, Prisma, Phoenix, gRPC, REST. Databases: PostgreSQL, Aurora, MySQL, MongoDB, DynamoDB, Redis. Cloud and DevOps: AWS (ECS, Fargate, EKS, EC2, VPC, IAM, CodeDeploy, CodePipeline), GCP (GKE, Compute Engine), Docker, Docker Compose, Kubernetes, Pulumi, Jenkins, GoCD, GitHub, Linux. Payments and contracts: Stripe, Paddle, PayPal, Oneflow, Scrive, BankID, ID06. AI: LLMs, RAG, AI agents, LangChain, LangGraph, OpenAI Agents SDK, Stack AI, Python-Goose. Observability: Prometheus, Grafana, Datadog. Testing: Jest, Playwright. Media and health: HLS, DASH, FHIR, HL7. WHAT WE NEED FROM YOU A short description of a past project that combined at least two of: accounts, maps, payments, real-time features or AI. Which of the technologies above you have used in production, which you have not, and how you would close the gaps. Your fixed price and timeline per milestone, your availability and your time zone. Links to a GitHub profile or live work.