To train a bespoke LLM takes a lot of effort and compute, you are perhaps better off using Retrieval Augmented Generation (RAG). Here's some information from Langchain

https://js.langchain.com/docs/modules/data_connection/ https://python.langchain.com/docs/modules/data_connection/

Also OpenAi last week released Assistants which is an easy way to achieve RAG without needing new tools such as Vector Db's. Although 5000 docs is perhaps to large for assistants.

The first decision is whether you would use an Open Model such as Llama2 and host that yourself or a Model such as GPT 4 from openAi or Claude2 from Anthropic etc.