First of all you just understands the job profile of all employee who are working in your organisation and after that you will provide the designation as per hie/her experience and salary then you will create the department.
after creating department you have data regarding create the salary structure and salary structure is internal decision it differ from industries to industries.
keeping all this in to consideration go ahead.Presently are you paying Consolidate Salary?
You cannot imagine things and go ahead as you like. First have a frank discussion with your bosses and try to know who are you, what are the aims and future plans, how and when you are going to take off etc. And importantly try to obtain a complete frame work, road map, fiscal & financial budgets atleast for the next 5 yrs if not for 10 years, without which your work will be meaningless. Draw appropriate charts and HR tree by which only you will get a clear idea as to how you can proceed. Likewise you should gain knowledge on the similar estt. existing in diff. parts of the country, abroad already running successfully. Future promises and growth opportunities (SWOT) etc. which will help you to exactly target at what. The charts and budgeting will determine how your man power should be read with financial budget. Discuss once your draft is ready with finance head before draw up your detailed man power planning.