From my experience in Florida, just be sure you're covered for flooding and drainage esp with a new highway, check your elevations, etc.

Instead of bookcases, go for elevated shelves.

When elevating Storage Units what rule of thumb do we use for estimated expenses? 

They will then give you a draft set of drawings, front & side elevations and floor plan. 

A Surveyor can ascertain exactly where you are in relation to the flood plain, by doing what is called an Elevation Certificate. 

If there's a child who lives in the unit who has an elevated blood level, even if it came from outside the unit, and you don't have the certificates, you're going to be target #1 and you won't be covered by insurance without the certificates.So just on that issue alone, yes, even if you have to put it on credit cards, I would get those new windows in, on all the units you're renting out.

Estimating costs for new phone floor/elevation, accounting for unknown costs/mistakes

Estimating all costs for new floor plan and elevation is not easy.

Although there was no elevated humidity or surface areas affected with mold, several of the air samples came back with very elevated levels.Almost immediately upon receiving this notice we offered to let them break their lease without penalty.

One corner of the property and the basement floor are about 3 feet below the base flood elevation.