The list to look for is extensive: mechanical, electrical, plumbing, structure, layout, terminate damage, mold......Can only be learned over time and after viewing multiple properties with and without issues.  

It was super helpful this last month when the power was out for 5 hours and they texted me and the guests.

we always hardwire ours but here's the gist of it....Smoke detectors must be hardwired or have 10-year battery after April 1, 2019Licensees should be aware that as of April 1, 2019, the new General Business Law Section 399-ccc requires all new or replacement smoke detectors in New York State to be powered by a 10-year, sealed, non-removable battery or hardwired to the home.

I bought a $3500 mobile home that was in great shape, paid 500 to get my electric pole set up and 45 to get them to put a tap in for water.

Mostof the hard work has been done, new septic, heat, AC, electric, plumbing and insulation.

Also you added the utilities as "other income" but the only expense you have for utility is electricity ($17 a month?). 

., electricity, gas, CapEx repairs). 

You'll likely want an entire estate plan drafted including wills and health care directives and powers of attorney, etc. as well. 

Keep in mind that the seller is going to try to get out from the property for a reason, just ask a question and listen, if he's motivated enough they will reveal more than needed OR they will not have enough selling points which could be a bad thing. ie; vacancy rates (leads to knowledge about the area or housing issues the tenants had), water usage (potential plumbing issues), appliances held in the units (leads to how old the electrical is in the home) CHECK IF THE OUTLETS ARE GROUNDED !!! 

In general, yes you can make them responsible for indoor plumbing, electrical, fixtures, appliances, etc.