You should have a robust insurance policy.

If you don't plan on paying cash and have to leverage with an owner-occupied loan product then you should set up your LLC as a property management company because you will not be able to borrow in the name of the LLC.  

We are considering becoming a private lender with them and I am doing some background research on him and his companies and wondering if anyone has done any deals with them.

Applicant credit scores should be treated with a high level of care and should not be handed out when they aren't assured that you are locking them up and taking due care with private and sensitive data.So, many places, including the screening company we used for years before moving to a PM, provide a suitability score rather than the actual credit score. 

A professional trustee such as Exeter Trust Company is the way to go if you want it done right, imo. 

Your primary insurance policy with $300,000 in liability coverage should be sufficient in 99.999% of all lawsuits.5The best protection for you and your investments?

Rules/policies are subject to change and selling units in some buildings can be challenging.Condos, on the other hand, typically have more lenient rules/policies oftentimes allowing for unit owners to rent their apartments immediately and indefinitely.The rule flexibility, however, comes with a price.

Regardless of which state you choose, be sure to maximize your liability on your renters policy and get an umbrella - this will protect you more than any LLC will. 

Plumbing company says its the only way to resolve the issue I have.

The specialist I recommend you have is an attorney to properly draft the documents and a title company to facilitate the deal.