Noob questions about Dev environments

I’m interested in a Pro account for the various image manipulation features.

But I don’t understand how I would work with in dev site using Cloudflare before I do a production release.

  • I use a online service to spin up dev environments that have random urls, how does this work if my Pro account is associated with www.mywebsite.com?
  • Have I got to use a sub domain e.g. mydevsite.mywebsite.com? In which case how to I prevent it from being publicly accessed?