i would have to assume your local soils are full of clay, requiring a fully grouted wall.Miami Dade as well as the rest of Florida follows the Florida Building Code, which is based on IBC & IRC.

It's possible that the tenants may have a case for what is called "constructive eviction", meaning that the property is not suitable for healthy habitation.

It is exposed to the elements and is just soil?

If its stabilized and you don't expect any major capital expenditures in the next 5-10 years such as a roof, furnace, or renovating any units then somewhere between 5-10% would be a healthy assumption. 

I would retain a healthy reserve account to cover vacancies and major repairs.

Like all things in the universe a balance is required for a healthy environment and my county is way off kilter in this area, presently.On the texas gc comment I would have to respectfully disagree(somewhat).

Your survey company is supposed to give a topographic survey telling you what the current elevation of the ground is, and then an engineer is to test your soil to tell you what you're building on.

Don't go with friends, find a professional and keep a healthy distance.

I don't want to get into a lengthy health insurance thing but as long as you are healthy you can get coverage.

As for contingencies, it would depend on the lot, the location, are there any soils reports or anything that have been done on the property yet?