My worry is that the property might fall into probate or tax auction once he passes and someone who knows someone will get the deal under contract before it reaches public offering.There is a real estate agent in the area that gets about 85% of all the listings in the micro-market, so she is farming these properties constantly. 

I found this deal off market and found agreeable terms with the seller involving a midterm lease during renovation.

My concern here is that depending on where your property is located, that might not be the market standard in that neighborhood.

Maybe % of purchase price (though that would mean low estimates for killer deals, and higher estimates for hot market properties)?

Hopefully along the way your properties appreciate, you pay down debts  (mortgages) from operating income, and you get market appreciation on what you can rent each unit for - giving you more income each month. 

Even with a single family often there are utilities that you will want to pay directly as a landlord and which are customary in that market to be included in the rent.

Before the market turns to good.4. 

I know the market fluctuates and that can be a factor, but generally speaking.

Made good money for a while then the market turned and he lost a lot of coin ...  

I'm Adolfo Dominguez from San Antonio Texas, I'm particularly passionate about investing in  the San Antonio area, I am a marine corp veteran who is here to learn and grow in this community and hopefully get some great advice  I am Excited to learn and connect with you all!.