WhatsApp-Native Salon Booking System Development

We need a freelance developer to build a WhatsApp-native appointment booking system for beauty salons and hairdressers. Customers book entirely by chatting to the salon's WhatsApp number — choosing a service, day and time, with the bot checking real-time availability and confirming only genuine open slots (no double-bookings). Salons manage everything — hours, staff, services, and bookings — from a simple web dashboard, and get notified instantly when a booking lands. The stack is WhatsApp Business Cloud API (direct with Meta, no reseller), n8n for the automation/backend logic, and PostgreSQL for the database, all self-hosted on free-tier cloud infrastructure — full technical spec is attached. The build must be multi-tenant from day one (so adding salon #2, #10, #50 is a config step, not a rebuild) and must have no recurring platform or licence costs — the only possible ongoing cost is Meta's own small per-message rate on optional reminders. We're looking for a fixed-price quote for the pilot build, plus your suggested rate for onboarding each additional salon afterward. Please share relevant n8n/WhatsApp API experience and a rough phased timeline with your application.