LLM based Copilot Assistant Architecture

hi Cole,
Great stuff you are building and sharing with us related to LLM, Agentic-ai and many more. I am working on product where want to introduce the LLM based copilot assistant to user. RAG+Database, the user query on user specific screen and guide and do conversion. First need to authenticate and authorize the user to have proper access or not. at a time multiple users from the different group and different information can asked. The copilot assist the user on user request.
I need your help to identify the best tech stack, framework to interact with user, fast and accurate response, secure, scalable, robust and fault tolerance AI system/architecture to build.
If you can break down this and share the architecture then would be helpful.
Thanks in advance!!
MHB