Haha, usually people use Google Analytics or something like that to know such info. Discourse dashboard has daily pageviews and user visits that can be used to approach that too.
Not true, your whole site is served via Cloudflare:
curl -I https://blenderartists.org/
HTTP/2 200
cf-cache-status: DYNAMIC
cf-request-id: 0a6ef945b3000002fe272b2000000001
server: cloudflare
cf-ray: 6591c4b5ec5902fe-MIA
alt-svc: h3-27=":443"; ma=86400, h3-28=":443"; ma=86400, h3-29=":443"; ma=86400, h3=":443"; ma=86400
But that may be completely unrelated as your nginx is complaining about upstream connections instead of downstream ones, which means it’s running out of connection between nginx ⟷ unicorn.
Since we keep an open connection for each visitor due to message_bus (live updates service), this is kinda expected if your site is somewhat popular.
Bumping the worker_processes and worker_connections is safe and sounds like it makes sense in your case. We default worker_processes to your number of CPU cores. How many CPU cores do you have?