Important Setup Steps for HCM HR and Payroll

I am thinking to acquire HCM.
Can any one who has a practical experience with HCM R12 guide me through the important setup steps to start HCM HR and Payroll.

My Organization hierarchy is:

Company : 1 to n companies, separate employee no, separate and independent payroll, separate data by company
Region: under company eg Eastern, Western,
Branch: 1 to n branches under a region
Department: 1 to n departments under a branch

Rest of all things directly related to employees and vary at employee level.

Thanks and best Regards
Javed