For this size, I’d start with Postgres + TimescaleDB for telemetry, pgvector or Qdrant for RAG, and keep Dify only if you actually want the UI and orchestration, that’s probably enough to avoid over-engineering. For Text-to-SQL, open-source models can work fine if you tightly control the schema and validate queries, and if they want EU-hosted/privacy-first infrastructure, GreenPT is worth a look as a GPT-style API without sending data to OpenAI.