Building an offline-first stack: Replacing Google Photos/Drive for local network continuity?

I am auditing my home network setup to prepare for potential extended internet blackouts. My core goal is ensuring that if the outside connection drops completely, my household retains full, native local access to our personal documents, files, and family photo libraries via the LAN.

I am looking to deploy a self-hosted stack on local hardware (considering a 2-bay NAS or a dedicated micro-server) to serve as a mirror/alternative to our Google ecosystem.

1. Photo Management: For those who have migrated from Google Photos to Immich or Nextcloud, how do they perform when completely disconnected from the internet? Do features like local facial recognition, timeline scrubbing, and mobile app caching hold up over a pure offline Wi-Fi connection?
2. File Synchronization: What is the preferred pipeline for continuously mirroring an active Google Drive back down to a local self-hosted instance so that the files are always structurally organized on-prem?
3. Client Access: Are you relying on local DNS overrides (like Pi-hole/AdGuard Home) to keep client mobile apps pointing seamlessly to your local server when external networks are unreachable?

Keen to hear from anyone who has successfully simulated a "WAN-down" scenario with their self-hosted stack and what bottlenecks you hit.

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