Nginx cache tuning / debug

Hello. I cache contents with NGINX proxy_cache in all my sites but I’m
not sure I’ve the best setup.

Are there rules/hints to properly set the size and/or the TTL for the
cache ?
Would be nice to have a tool that monitor/track files written in the
cache and those deleted (an the reason as well)

Is there such a tool or can I enable some logging feature to get these
data ?