On the plus side, it won't show up on your personal credit report.

I have read varying articles saying between 1.5 and 7%3) How do we determine the monthly rent and rent credit?  

Family says original quit claim deed is fraudulent.

(It doesn’t sound like you willingly misled or fraudulently did anything.)If he really thinks he has a case he’ll talk to a lawyer.

Should I do a Line of Credit on one of the warehouses?

The local bank will evaluate on its value and your credit risk,  you will have to have 20% (approx) down though. 

I would be more open on using creative financing especially if you have good credit and income you can use that to leverage your way into deals with the principle.

Should I do a Line of Credit on one of the warehouses?

For tenant management, billing, expenses, background/credit checks - HIGHLY recommend Buildium.

If your business entity has a history of cash flow you could look at getting a business life of credit is another idea.A creative thought is maybe ask the seller for a concession and have them seller  finance the down payment for you that way you are creating some extra money for them as well as granting them some extra income that they would be losing from the sale of the property.