how much to paint a 1400 square-foot interior all white trim and walls?

She put a new shingle roof, new power pole, all new siding and skirting (looks like a new MH), new windows, and stripped all the interior walls to the studs. 

Correct, the interior is old and dated.

The interior is very outdated and is in need of quite a bit of cosmetic work (paint, carpet, etc.).

Fortune favors the bold.I am spending about $1,500 right now to improve some small interior design details that will make it even more attractive to renters.

In addition to renovating the interiors of our 53 units at each turn over, we are (now) doing 3-4 roofs per year and the same number of HVAC units.

You need a local team of:-Real Estate Agent-General Contractor-Interior Designer-ArchitectA good general contractor who thoroughly understands your renovation plan will be able to oversee the entire construction process, and execute on you/your designers vision.Just be available for occasional FaceTime calls in the event there is anything that they need your input on at the site.There are some budget contractors out there who require a bit more "hand holding" but they would not be a good fit for somebody investing from a long distance.

These properties are usually 25+ years old and have deferred maintenance issues and are located in more difficult areas as well as needing big capital expenditure investments (new roof, interior remodels, etc.) to remain competitive.

The buckling on the interior wall is a new one to me though....

The house is a half duplex newly renovated interior nice backyard with a porch, drive way, and unfinished basement which I see as potential value or forced appreciation when we decide to finish it.