My first concern would be, are you sure it's a "deal?" I know it's a portfolio of 60 units, but that doesn't mean it's a "deal." You said he is open to "reasonable" offers, but what does that mean to him ...and you. A reasonable offer to him may be a non-deal for you. Evaluating a potential deal like this takes quite a bit of time and energy, and may lead to a dead end.
So, what would you want out of this deal? Below market price? Above market return/cashflow? Would you want to profit from the sell some of the units and keep the rest, or? I would get clearer on your intentions, and then evaluate his motivations, and see if you can make them align. Otherwise, you may be going down a route leading to nowhere.
So far, nothing you wrote hints to him being motivated to sell below market. They are class A properties, 100% rented close to market rents. That sounds more like a dream for him as an investor with no evident reason for him to accept a discounted price or terms. I know he's older, but why wouldn't he want to pass them on to his son or family?
Anyway, to evaluate the portfolio, I would first get all the addresses and financials for at least the past 2 years. We get the financials on multi-fam properties (5+ units) and just the rental amounts and terms for the <4 unit properties, to start. Then put it all on spreadsheet/s. Evaluate the 1-4 unit properties for value (find comps), list current scheduled rents, estimated vacancy/collections, expenses, etc and you can have another column for a proforma, if rents could be raised, etc.
For the 5+ unit properties, you need to determine the market cap rates for the area and compare them to the actual performing cap rate of the Subject properties. This is why you get the financials, to see what the actual #'s are. Then you can evaluate if there is room to improve, what discount you would need, etc.
But, for me, there would really be no reason to spend the time walking the properties first. I would just assume average condition for the units to evaluate them, until you could verify that. But, without being clear on motivations and if there is a potential deal here, walking the properties may just be exercise.