Let me answer my own question so far.
Basically I followed this forum post for 16.04 to 18.04
and then followed my own advice from back then to update the repository using the script located here: Download and install GitLab | GitLab
Things seem to be working just fine. Do note that my CE install is super basic - we just use it for Git and nothing else - no CI/CD, etc. so I can’t speak to how that might go - buyer beware.