Dedicated servers for hot content with unmetered connections caching user generated content backed by Cloudflare R2 (no egress charge and CF will want $$$ for non HTML CDN serving) or Backblaze B2. Store metadata in a relational database like PostgreSQL for caching servers and clients.

A rough proxy as described is a few hundred lines of Python.

https://news.ycombinator.com/item?id=28682458