Tired Landlord "Buying a portfolio"

I've recently come across an older landlord that appears to be selling off some of his rentals. After doing a little research last night he appears to have been buying and holding since the early 80'S and hold's between 75 to 100 properties as of today. The research shows that about 80% of them appear to have no mortgage or liens on the properties. He has a good mix of Single Family and Multi Family.

My question is what is the bet way to approach him about buying a majority of his properties rather than the few he has on MLS?

And what is the best way to analyze all the properties?