Only purchase the property if the seller removes the tank and tests the soil, and a clean bill of health is given.

I have a contingency in place for the soil test to ensure there is no contamination, but as it's fully operational does it make sense to immediately remove the tank and install an alternative heating source? 

As a result of that, whenever someone needs to buy a home from this area, they'll need to find a good home inspector that can figure out if there is a stream of water flowing underneath the basement or not. 

Duplex up, with the caveat that I'm assuming you are building on a site with decent soil conditions and that you aren't seeing any issues with the height limits in the your projects zone.

A property I own has a front porch and is not properly supported underneath, so basically the whole structure is leaning forward.

Ground shifts a lot all over town due to our soft clay soil and some areas can be worst than others. 

What is underneath this area?

If made out to someone other than myself, not used, the procedure at my bank, "Citibank", is to on the back of the check, write in "Not used as intended", sign underneath it, and deposit to the your account.

Filipe it is in North Carolina so definitely soil is optimal here for flowers, trees etc.

Here are the key items you need to address before the land is purchased;You will need PERC testing to determine if the land/soil can support septic and absorb water.