Just be careful, understand that if you do a PULL only CDN, you're not going to gain big benefits. If you do want a pull only CDN, have a background task runner to retrieve the files, and update them locally.
Sure. I have Nginx set to keep files around for s long time and serve stale and refresh in the background, but proactively refreshing periodically is a good idea.
This statement makes no sense. A CDN edge node is just a cache; its size and your access patterns determine the hit ratio.
At $dayjob we get Nginx cache hit ratios on our edge in excess of 99% for “an origin fetch” setup. That is a very large benefit.
Cloudflare works entirely on origin fetch. They seem to be doing okay.