For example September is always slow right after summer ends. 

Will the insatiable demand for this slow down ?   

The contractor isnt your enemy , he is there to give you a finished product at an agreed price .

In an environment like that, someone could get started and then scale slow.  

(We personally do portfolio and single property loans and will be adding a HELOC product soon!)

Better quality product, better installation, and making relationships is invaluable if you plan to scale.

(the way the conventional mortgage was a root canal)I am probably going to pay cash for the property upfront and then finance it after the close, so I have some time to explore financing products. 

hold some of that initial 100,000$ for reserves. if you spend it all and something goes wrong you wont have time to accumulate profit the first year to really afford to fix anything. then you'd be dependent on personal income or another loan to fix the issue if one arose. play it slow and safe at first while you figure out the game and take some initial hard knocks that are bound to come. 

Please try to suggest products/services that you have used and like. 

The Vanderbilts who were as wealthy as the Rockefellers at the time did not use this strategy and eventually their net worth evaporated due to many things.Unless you have a license to sell life insurance and know how to structure the policy for the client's goals, you shouldn't be knocking products that can and do benefit MANY people -  especially those who have maxed out other tax deferred accounts.By the way fees are paid over the life of the policy, not all up front.