How to evaluate tasks in a usability test?

I need to do a usability test with 5 participants +- for a system that is like a content mangagement system with crud operations and things like that. So for this I created 5 tasks and now Im with some doubts about a proper way to evaluate them.

Maybe a good way to test the system is verify if the user achieved the goal of the task, then also how hard it was to complete the task, that is the number of necessary actions compared to a otimal number and also the time to achieve the task.

Do you know if this metrics are ok a to do a correct usability test? And if is important to add some more metrics to the test or also if some of the refereed metrics are not very useful for an usability test?