Which model for technical documentation?

Looking to create high level / low level designs (software), based on existing templates/examples, cross reference code, use mcp to download confluence/jira data - also plug into agentic ‘coding’ frameworks opencode .

I mostly use opus 3.6 with Kiro-cli , but I want my data private. What options do I have? Do I really need 4x 3090 for this level of reasoning? I also need at least 256k context.