Usually a signed CDN URL that expires; copy it to your own storage.
Subscribers on YouTube, followers elsewhere. null when the platform hides the count (a YouTube channel can); never 0 in that case, so a follower gate can tell "unknown" from "none".
Platform extras, display-only: keys differ per platform, so never filter or sort on them.
The platform's own id. Stable across renames — key on it, not username. null when the platform doesn't return one.
Public handle. Mutable, and a freed handle can be taken by someone else.
A connected account's profile and audience.