What are key KPI's to optimize the warehouse Overall performance ?

I think if we want to identify KPIs for warehouse  

1- we must know  are we follow a best practises in store processes ? 

2- we must know  where is the gab in the processes and how we can close it 

3- focus on period for each process in the ware house 

4-  make every process in warehouse is an countable and measurable by time or by number .