CR had put significant $$ into renovations so these row houses were really like all new - roof, appliances, gutted throughout etc. it was understood that many of the rentals would be Section 8 which is a good secure investment.

In the words of famed real estate mogul / investor Barbara Corcoran:"If rates go down just another percentage point, that's what I'm hoping for by year-end, prices are going to go through the roof...Everyone will come out and buy.

Then we had a bunch of cap ex (roof, water heater, appliances) all needing to be replaced within a 2 year period.

I think that roof design will cause you future grief. pass.

Asking the sellers to repair the whole roof is quite common, sometimes their insurance company will repair it for them!

. -- You'll keep back maybe 5% of all rents for routine maintenance and another 5% for capX (big expenses like roof or furnace replacement).  

You get SOME advantage of economy of scale on a 2-4 units like sharing the roof, one foundation, etc, however single family tenants are generally more caring of the house.

Is it ok to place metal roof over shingles?  

According to the inspection, a replacement job must be completed on the roof, windows, doors, siding, soffits, back deck, and front porch, to name a few (which one should I even start with?).

Even if, say, the roof needs replaced, but it isn't currently leaking and keeping you from renting the unit, then you can punt that option, at least for a bit.And I also second Rob's take on going straight to the contractors.