The first time, we actually found (the manager never noticed) where the tenant moved the gutter drain spout to where it was flowing under the HVAC pad, eroding the soil under it.  

The shower floor that was in there was fiberglass with foam underneath.

It is a very common problem in my area with our soils and the older houses that have block walls that were never reinforced.Steel I beams are common because if the wall isn't bowed bad, it saves a lot money compared to digging out the wall and either pushing it back and reinforcing it or laying a new one.

Again check out the BP calcs as they are a wonderful way to get some numbers underneath you and it will illuminate what other pieces of information you will still need to figure out.

Once a tax lien is placed on the property, can the county/tax lien holder take the property out from underneath the note holder if the borrower continues to defer his taxes?

I am not experienced in such developments, but your situation made me think ... to fit as many parking spaces on the lot as possible without sacrificing building square footage, one option is ground level parking underneath the structure.

Make sure it's not something out of your control (soft soils, sinkhole, etc) that will cause reaccuring problems. 

I have asked a lawn care company about sodding it just to get ideas and it will be very costly and they also cannot guarantee that the sod will last due to 1) large trees causing shade and sucking all of the moisture out of the ground and 2) poor soil in that area.

You can put an underpayment underneath it if you want.  

Some topics that have been brought to my attention are:-timber sales, soil mining, solar power generation (solar farming)As of now, there are two separate tracts of land with potential opportunity in two separate states in the SE (USA) I am looking at.