For example, if you open a wall / expose and old wiring (specifically Knob and Tube) you must remediate all of it to get any insurance company to give you a policy.

How do I do my due diligence in confirming and or remediating if needed?

That issue should have been remedied at closing. 

Most have already tried to find a way to remedy the foreclosure by working with the bank, tried Mofiication Gurus, explored bankruptcy, and even shortsales.

Owner had to do a lead cleanup a couple years ago b/c of CMHA, and it was professionally remediated.

For example I found one for $35K, but it needs a new roof $6K and has to have mold removal, and remediation.

Hiring a certified mold restoration company (can be $$) sometimes is needed as some buyers want the assurance that the mold was remediated properly.

If they trash your unit you have judicial remedies even if you are required to return the security deposit but it will take time, money, and you will probably never recover damages from people who would do that type of thing.

He stated that OP is not working up to his expectations and let many of his investors down, in order to remedy the situation he proposed my property transfered to Blue Sky - his own management company assuring me that he will finish the renovation and rent it out.Kate Federico from Blue Sky took over in April 2018 - after few days she reported that the property is 70% completed.

There was some remediation in the basement  that had to be done which I had my guy step in and do.