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.

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.

The effort included a retaining wall design, grading plan, water/ sewer, underground utilities, pollution controls, drainage, quantity of materials and construction specifications.

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.

There are so many items you need to check on a mobile home park in due diligence and we wrote a course around it.Here is a short list of the most "deal-killing" items:1) Test ad.2) Certificate of Zoning from the city or county.3) Phase I environmental report.4) Review of last 3 years of P&L (and tax returns if available).5) Forward forecasting budget.6) Rent roll and payment history.7) Review of the water, sewer and electric systems.8) Size of each lot.9) Confirmation of which homes are occupied and which are vacant.10) Rent comps on all competing mobile home parks.11) Study of the metro market.12) Survey and title.Mobile home parks are much more complicated than they look.

I'd suggest hiring a professional or really digging into this yourself.My background: over 8 years in environmental consulting (13-present), 6-7 yrs doing floodplain development permitting across the country for telecommunications, commercial real estate, and oil & gas.

I’m just trying to get a feel for how some of you vet tenants and the environmental you utilize so I can be more precise when I’m ready to pull the trigger 

I graduated from the University of South Carolina with a degree in Civil and Environmental Engineering in 2019 and currently work as a Land Development Engineer (EIT) with a global architecture, engineering and construction firm.