How can I create Jira template for Epics with multiple tasks (not sub-tasks) in it?
Sure, you can do that on with Easy Templates for Jira Cloud version. Read How: Epic Templates
This feature, however, is not av available on Server/DC edition yet.
How can I help a team to better troubleshoot an error
...
Can I use a template saved from Company-Managed project in Team-Managed Project?
You can use Jira task templates in team-managed projects. However, there’re some limitations. Here how it works.
...