First Days Migrating from Wink to Hubitat, Successes, Failures, and Solutions to Help Others…

Short answer is external communications are hub firmware update checks, nightly maintenance, and NTP checks.. once you get your system setup you could just block the hub from external access - you'll still want LAN access of course. The only issue you might have is time drift so using the community based NTP driver can take care of that..

Consider installing the community Hubitat Package Manager - it allows for easy management/updates of various community apps and drivers.