WhatsApp AI Lead-Capture Chatbot

I need an AI-powered assistant inside my WhatsApp Business account that greets prospects, answers their routine questions, and—most importantly—captures and stores their contact details so I can follow up. My public site is built with custom HTML/CSS, yet for the first release the chatbot will operate only on WhatsApp; future updates may extend it to the website once the core flow is proven.

Key goals
• Lead collection is the top priority. Each conversation should finish by saving the visitor’s name, email, phone, and the product or service they’re interested in. A simple dashboard or Google Sheet is fine for v1, provided the data is export-ready for a CRM.
• Natural, fast replies powered by ChatGPT (OpenAI API) trained on my FAQs, PDFs, and website copy.
• Seamless human handoff when a question falls outside the knowledge base.
• Optional appointment-booking hook (Calendly or a native calendar API) so qualified leads can set a call on the spot.
• Scalable architecture that lets me add more intents, languages, or channels later without a full rebuild.

Tech preferences
You can use the WhatsApp Cloud API, Twilio, or another reliable gateway. I’m open to a no-code stack (e.g., Make, Zapier, Dialogflow) or a custom Node/Python build—whichever delivers a stable, low-latency experience and is easy for me to tweak after hand-over.

What I’d like from you
1. A short note showing at least one WhatsApp chatbot you’ve shipped, the tools you used, and any metrics you can share.
2. Your proposed stack and why you recommend it for this project.
3. A realistic timeline with milestones from kickoff to live launch.
4. A cost estimate that breaks down setup, testing, and post-launch support.

I’m looking for a clean, production-ready implementation I can grow with, and I have more automation work lined up if this engagement goes well.