My philosophy with contractors (in the past) has been - "hire the right people and stay out of their way".I need an honest, reliable, cost-conscious GC who can pull permits, demo and knock this "fix n flip" out in 3-4 months.  

As you noted, we don't go "out of our way" to mention that we didn't do something, but we are also very conscious to provide accurate descriptions of what was done.  

My house was fully renovated, but lower end neighborhoods are a lot more price conscious and are not willing to pay a premium for a nicer place.

(my background: been doing wetland delineations and permitting in the gulf coast states for 10 years)I'd recommend you contact a local environmental consultant on that one.

May answer as to what you need to know before you make an offer is basically "everything" with the exception of less than obvious defects to the structure or situations that need environmental testing.

The reserves will be more so for big ticket items in the future but I'll be very conscious of using it for when the market presents an opportunity.  

Pretty much every Phase I or II environmental site assessment I've ever seen references past studies, and not just studies done by the same company.

Some cost that may vary based on location will be your environmental impact study, your list of cost from the Architect may see a lower cost for the schematics on a smaller project, with similar footprints for all four units, versus varying unit size, and scope requirements (less work, lower cost for A&E), the feasibility study, proforma, 3-D renderings, and other associated cost are going to depend on where this project is going to be built. 

In most places for almost anything permanent that isn't ag (storage barn, planting, etc), you will likely need to either engineer to meet floodplain requirements/permitting or find somewhere else.Happy to take a look at it if you DM me the location, my W2 is environmental consulting and I've done floodplain development permitting for about 7 years, mostly in TX and the gulf states.

The best you would be able to get is a Letter of Environmental Protection, which tells everyone you did illegal work then hired a licensed deleader in to fix it.