Even with holes/tarp on roof and plywood over windows, the place still smelled like smoke. 

The deal that pays all your costs may also come with tons of repairs or problems so its ok to buy a nicer property that will not need a new roof furnace well pump sceptic etc... in the next five years.

., testing main components, general mechanicals condition, basic roof condition, any major red flags, etc.) for a lower cost.

I have a few questions about handling this situation:- should I hire and pay for a plumber to go into their unit to cut open the ceiling and identify the source of the leak? 

I strongly recommend not getting a refrigerator with a water hookup they often leak and damage the floor or the downstairs unit or attract mice to the source of water.

. - New tenet fees - Small toilet leak (should’ve barely changed things)After those bullet points, no explanation for low cashflow. 

But you are talking the roof will get ripped off, etc.  

Can you imagine how much it costs to put a roof on that place?!    

In my experience, relying solely on pictures can be outright misleading, they do not provide insights into the internal structures or the condition of the roof, plumbing, and wiring to say the least.

I do like the fact there is everything under one roof.