BUT, I had to put on a new roof which I didn't think I needed.

Lots of things come immediately to mind:  Septic problems, a new roof, HVAC failure, lower-than-projected rents. 

and most of the time is  bad management, bought the wrong price, Interest and Insurance to the roof and, I cant get out the Bridge loan to do a DSCR loan etc ...Simple hands on, work do research and minimize risk. 

Rent paid for all of the expenses, so it cost me nothing and over the years (I kept it for ~20 years) price almost tripled by the time I sold it.Not sure what grad program is 3 years (I'm used to 2 for masters, 4 for PhD), but if you do need to sell one, I'd look at each property and see which one has the most equity, highest interest rates, lowest return, major expenses in the near future (eg new roof) and you mentioned you'd lived in two for 2 of the last 5 years, so have capital gains exemptions. 

Outside of real estate I am in the construction industry, in Commercial / Residential Roofing.

That’s perhaps a B area.Do you see 6 inch tall grass, moldy siding, and damaged roofs here and there?

The roof is fine until it leaks, decks are fine until they are not, things wear out, line blockages don't happen overnight they most often are buildups over time until the result IS seen overnight. 

5) Why was new roof NEEDED?

I did talk to a couple trying to buy a $1.4+ million duplex/2 level flat here and house hack it (they were outbid). 

In these instances, you'd have to check things like flooring, plumbing for leaks, roof for leaks, hot water heater, and heating and air conditioning units.