Setting up multi-tiered accounts, contacts and leads

Setting up multi-tiered accounts, contacts and leads

I'm just getting started and want to set up the accounts, contacts and leads correctly but don't know where to begin.  Here is my dilemma:
 
I five or six main lead threads that branch down several levels.  I want to keep them all separate so I can communicate with them differenly so I don't want to throw them into the same category.
 
Ex.Government
Main category (account?) HHS- under that NIH and several others- under NIH- Cancer research & others
Another main category USDA- under that Forest Service and others- under FS regional reps
And so on..
 
I also have state governments like Virginia and WV.  How do I create separate "trees" whose roots fork off the main to form subsets of the whole?
 
And then there are private groups like Motorcoach operators who are a seperate sales opportunity.
 
I just can't translate what I have on paper to the categories with Zoho- Help!