Full Custom Real Estate CRM + Marketing Hub Platform (Multi-Tenant SaaS, GHL Backend)

We're building a multi-tenant real estate brokerage platform — a fully custom CRM and Marketing Hub interface, with GoHighLevel running invisibly behind it as the data/API backend (no native GHL screens shown to end users). Detailed specs and mockups already exist for the majority of the build. Core scope: a custom login/auth system with per-agent tenant isolation (each agent gets fully private, isolated data — not visible to other agents or admins, even in aggregate), a custom CRM interface (contacts, pipeline, dashboard, goals) built against GHL's API, and a full Marketing Hub tool suite (flyer/postcard/email/newsletter builders, business cards, letterhead, social media tools, open house tools, listing presentation deck, admin CMS) — most already fully spec'd and mocked up. Strong candidates have experience with: multi-tenant SaaS architecture and strict data isolation, GoHighLevel's API/webhooks, custom auth systems (server-side login handoff), and ideally real estate/MLS-adjacent integrations. Milestone-based engagement preferred. Full specs, architecture docs, and design files shared with candidates under NDA once we move past initial screening. To apply: share relevant multi-tenant SaaS / custom auth experience, similar past work, your rate structure, and your availability for a multi-milestone project.