This is to protect you from day 1 not being deeply under water.Seller financing is better if you won';t qualify for a bank mortgage, some times the seller will ask for less down than a bank.Bank financing is always cheaper, lower interest rate, price is always verified by an appraiser, but you need to go through the frustrating closing process of under writing all your doc.

The first couple of things you have to do is to set up your company as a corporation of some type to protect you personally and find/get a local Team put together that will return your phone calls.  

Land owners have legal rights that are superior to buyers, title ownership is protected more so with real property than personal property.

@Andy K  Here is a very good reference from the Environmental Protection Agency.  

All of these properties are traditionally financed, 30 yr term, with no outside investment (except the first house with my brother).I'd buy again in Tennessee, but I think I need to improve my legal protection and lease.  

Can we protect ourselves from the owner deciding to sell in the case we do rent to own?

Many times, standard form contracts you may find as part of your organization are not sufficient to protect you.

We are looking into switching to modular construction to shorten the construction process.  

A local attorney will also explain to you what practices and procedures you must follow in order to be sure the LLC (the LLC won't do you any good if you don't know what you have to do to maintain the protection it is intended to provide).

Have you set up your company as some type of corporation to protect yourself?