Kitchen Walls are Formica (might sheetrock over or paint), living areas are wood paneling, bedrooms are sheetrock if that matters. 

He has the tenants put the check inside the electric panel and goes by on the 1st of every month to pick them up.

A DW will have TWO steel beams down the center of the house, bolted together.Somewhere on a DW there is a kaers mark, sometime this is on the electric panel.

Electrical: check for knob and tube, aluminum wiring, Federal Pacific Electric panels or old fuse boxes, ungrounded outlets, lack of GFCI's etc. 

There is a lot more that goes into having a secondary dwelling space in the same home.Separation between the spaces usually has rules, like double fireblock drywall, sometimes a separate electrical sub panel, etc.So, if you are using it for guests, it could bring some scrutiny from the city/county when you go to apply for the permit.

I would be more worried about hail, especially with those solar panels, and especially without a garage for the cars.You’ll never recover the solar panels investment (or whoever installed them) as they are shaded by the big trees in the front.

What about joists incorrectly installed, floors that weren't leveled correctly, flashing installed incorrectly, electric panel boxes that are faulty, driveways installed without expansion joints (I bought a house that had a foundation that was shifted the first summer because of the driveway expanding. 

New to Mid life mechanicals in place (Water heater, electric panels, furnaces), no foundation issues (with a condition of accepting damp basements, nature of the typical stack stone foundation popular in the area), no major exterior defects (didn't want to deal with roofing going into winter), rent ready (legally had to accept tenants in place of course).

If the pressure doesn't hold or you notice water being forced out of any pipes, you know it may have plumbing issues.For electrical, FHA inspectors use a generator connected to the power panel.

IE, is there return in updating the old heating and cooling systems, or adding beds/baths, or interior updates (why everyone wanted to use wood paneling is compelling beyond me!)?