The big question is there any soil contamination and if there is to what extent.

In my opinion, there's no excuse for staying in his property and not paying the rent other than being denied safe/peacable and or healthy/sanitary habitation.

As it stands, this project has enough margin to cover the extra expenses and I will still make a healthy profit.

I hardly sleep, am barely present for anything and anyone and think that this is literally going to worsen my already somewhat compromised health. I

Basically, he knew before the owner would realize they would have to sell their business for health reasons.The drug store owner had a healthy side business as a Business Broker and made way more money brokering businesses than he did as a pharmacist.

I'd recommend that you study up on healthy LTV (loan to value) and come up with a percentage that you feel comfortable at. 

Since soil conditions, grade, rainfall and runoff, etc vary so greally from locale to locale, you need someone from that area to consult. 

That is why I have a personal umbrella policy for my personal dealings and healthy insurance on my business too.

Some builders don't include fees for plans, renderings, soil samples, landscaping, etc.

You may have to get on a list to be able to rent out your unit.Also... ensure the reserve is healthy if the building is old.