Ignore the marketing BS where they pretend to be "private money," that's the same as the guy at the car dealership pretending to be your friend.TLDR: A private lender is someone you already know and will generally beat a HML, who in turn is someone you don't know that is out to maximize profit and minimize risk.

I would take out ALL metal plumbing and update waste pipe to PVC and supply to pex.HERE, we have a lot of rust, calcium deposits, and lime, besides grit ruining faucets etc. 

To me it seems minimal.

It's not easy to do it right so that you minimize risk due to the amount of time you need to spend researching.

Going all in is fine, but minimizing risk and making sure you know your numbers is important. 

We’ve heard on the podcasts how you should really get to know the seller when attempting seller financing, but we also don’t want to waste anyone’s time.

You're wasting your time trying to help someone that doesn't really want to be helped.

Just as an example, what if it turns out there was contamination somewhere because the office was careless in how waste was handled? 

Back to the original question - I think one LLC would be sufficient in this case, it allows you to have the appropriate protection and minimizes the operating costs of the LLC.

That way the local partner can manage the property and therefore minimize expenses/maximize profits with the hands-on attention real estate rentals require.