A go-to method is to ingest different chunksizes based on the document hierarchy & then use langchain with a bunch of retrievers depending on the doc type.

Then create an index about the metadata of each doc. So that you can ask the RAGbot what all it can answer about.

Another way to ensure it stays on-domain is to generate synthetic questions & check for similarity against user queries. There's a whole rabbit hole of query decomposition to avoid straying off topic as well.