I can help a little with this one.
First, there's an options manager setting that controls if the template will be filtered by the customer's organization --- uninstall that option (and restart services).
We also have the assignee as a required attribute for the resolved/closed statuses. So to get around the 'assignee' always being the assignee of the ticket that the template was created from, I create a ticket that will be used as a template, and briefly remove the assignee as being 'required' when I close that ticket - and then put the requirement back on. This allows the template to have an empty assignee when it's used for a new ticket. Then the person using the template can assign the ticket to themselves.
But I've not found any way to have a template remain in an 'open' status, without having that ticket remain forever open. So all of our templates are in the closed status.
Hope that helps some!
Tammy