We separated and updated the utilities.

I will say that I have a long track record as a customer and borrower along with excellent credit. 

And if he wants to continue to be a customer of your business then he needs to realize that it isn't a charity house.

I thought about utilizing that property for storage space.

So, I would basically consider it an up/down duplex that does not have separate utilities.

Therefore we look out for their best interest as well as the help, safety and welfare of the public/anyone whom will utilize the space(s).  

Get those CCs paid down, and you'll also potentially earn higher credit limits on those existing cards (a good rule of thumb is to keep your utilization lower than 30% of your limit which, if done consistently, can boost your credit score). 

.+ Your customers will thank you.

Does it make sense to include internet with the utilities (that I already pay) to possibly rent my units for more money than similar properties?

You provide the space and utilities.