Due to the nature of property managemnet business which the accounting can get a bit complicated, regardless of which software you choose, I think it'll have some mechanical and tedious nature to it. 

By our nature, we are creatures of habit.

Each of these are valid approaches but the appropriateness of each depends on the true nature of the transaction and the motives of the buyer and big seller. 

"Weasel clauses" are by their nature unethical--legal, yes, but unethical, because they demonstrate that you never were in earnest about purchasing on the terms you offered. 

I think his methodology is as much human nature as it is financial.

It seems like a natural succession for a large multifamily unit owner to also own their property management company.  

The exact nature of your legal situation will depend on many facts not known to me at this time.

You may want to look into something of that nature

Let a mentor-student relationship grow naturally.

I think the answer to the essence of what you're getting at here will be revealed by:1) What is the nature of this "little business" that you're starting?