I was also going to suggest turning the water off from the inside. 

It is brick exterior with casement window and has water damage beside the windows (interior plaster is flaking/bulging).

(For example, upgrading water service or wiring or a new roof for the  entire building, a proportionate percentage of that should be a QRE toward the rental unit.)

You remediate the exact problem - mold comes from water leaks/intrusion - and forget about the rest of it.

The specific units I'm looking at are 1 BR/1 BA with a water view and poolsCan sleep anywhere from 2-6 with the addition of a pull out couch and a small bunk area for families$220K (Unrenovated) - $250K (Renovated) Similar units in the same building rented for $29K (this year) but "Closer to $36K in a stable year" (per management) My guesstimated costs will be $1500-2000 monthly using a 10% down vacation home loan, I'm considering using this management company at 26%The location is Tybee Island, Georgia.

If you can put mobile homes on your land, then you'll have to start figuring in costs to acquire the homes, pay for the move, and hook ups (i.e. water, electrical, gas, etc). 

It has 2BR/2B, 2BR/1B and the last one as an efficiency.

On top of that we are staying current with local/regional/national trends and data, as well as always working on working on making our business more efficient and effective. 

I realize the holding costs will be greater with a longer rehab period, but I assume it will be hard to rent up units while conducting major rehab work, while also reducing the efficiency of contractors ability to complete jobs in fell swoops...Thank you all in advance!

My wife has stories of washing dishes using a large tub, and taking cold showers with water borrowed from our neighbor's hose, during the time our water was off to redo the plumbing!