Employee and customer wise cost

  Hello Experts

Below are my business scenario

1.I want capture the employee wise cost so What  could be best way to capture  the employee wise expense in the below method

    Employee as cost center

    Employee as Vendor

    Employee as internal order

   IF anybody provide me advantages and disadvantage it will be  better understanding

2. Another one of my requirement in my  business scenario  customer group wise  COPA report with  net profit  level

Here GP level I will get it from my billing document(Revenue – COGS),  customer wise expenses I am going to capture through the cost center 

finally  I want  to settle this cost to customer group (COPA)

Is it Possible  ?

Thanks & Regards

Sri.