Congrats for your new job...!
As you are HR Manager you have define about your KPI. I can say this in simple manner The objectives of HR and the Outcome. KPI is an measurement tool where you can analyze your objective with output. KRA is the area to match with your outcome.
As an HR Manager - objective is close with business growth and strategy to improve the manpower and complete utilization of employee. We have to analyze the outcome based on input you given.
your strategy to closely mingle with business goals.
This subject of KPIs recur time and again. Just recently I had given my reply in similar post. I request you to go through the following link:
Though the heading of the above post is about IT company, the reply is applicable to all the industries. In the link above, you will find further few more links. I recommend you going through all the links patiently. This will help you in clearing your misgivings if any, on the subject of PMS.
Developing competence on designing KPIs is a time taking process. It requires working under some expert. Else, you may carry some misgivings and it becomes quite difficult to erase after holding some senior position.