I called my lender and expressed my concern to which she said she would ask the senior loan originator.

I personally would not co-sign or co-borrow with anyone, other than my wife, without a legal binding agreement addressing default or dissolution of the partnership.

Think of all the things that could go wrong and see if the lease addresses them: unauthorized pets or tenants, early termination, security deposit, lease violations, late rent, eviction, lawn maintenance, parking, etc.5.

I have their information in terms of address, but I'm curious to know why no one has placed a bid on the property. 

No one has asked me for it and they send 1099s to my home state address.

My question is concerning whether or not is can be a good idea to separate your real estate operations into two entities: (1) an LLC that holds your property and (2) the LLC that holds your property management operations, where the LLC (holding the property) would pay a management fee to the LLC (holding the property management operations) for its services. 

My other large concern is with budgeting.

I am mainly concerned with the Houston market.

I understand your concerns about the Series LLC, but decided in favor that option, since I'm going to wind up with 8-10 owner finance loans under the solo 401k, and 8-10 individual LLCs seems cumbersome and expensive.  

I definitely agree with everything @Caleb Heimsoth said. 5.2% is very low as far as historical standards are concerned.