React + Supabase + Stripe + Xero — staged rebuild of live UK construction SaaS

I run a construction company in the UK and I've built my own construction management software — project budgets, monthly valuations, client portals and PDF document generation. It's live and working, and I use it in my own business daily. I built it myself as a non-technical founder, and it's now at the point where it needs a professional developer to bring it up to commercial standard so I can sell it to other builders. The work is fixed price, split into four staged milestones: Migrate my single-file React app (Babel-standalone, around 6,000 lines) into a properly structured Vite + React project, with tests on the financial calculations Stripe subscription enforcement — webhooks, token-gated account activation, and revoking access when someone cancels Xero integration (v1) — OAuth connection, pushing my sales invoices into Xero, and importing bills from Xero New-customer onboarding — a seeded example project, welcome checklist, and branded client login links The backend is Supabase (Postgres, Auth, RLS, Edge Functions) and stays. Hosting is Netlify and stays. This is a rebuild and extension, not a redesign — the product must look and behave exactly as it does now, except where the scope says otherwise. I'll share a detailed scope document with acceptance criteria for each stage with shortlisted candidates once an NDA is signed. Payment is per milestone, released when I've personally tested and accepted each stage. All accounts, code and IP stay in my name. In your proposal, please answer these five things: Your experience with Supabase (RLS and Edge Functions specifically) and Stripe webhooks Have you built a Xero (or other accounting API) integration? Give me one example One relevant past project — link or description Your availability and time zone — I need at least 3–4 hours overlap with UK working hours for screen-share sessions Your recommendation, in one plain-English paragraph: JavaScript or TypeScript for the migration, and why If your proposal doesn't answer these five points I won't consider it. I'm a hands-on client — I test everything myself, I reply quickly, and I pay promptly on acceptance. I manage subcontractors for a living, so I work well with people who communicate straight and deliver what they price.