People in 1981/1982 were angry they were paying 18% interest.

You also need to consider that at a lower percentage of money down you will be paying a Mortgage Insurance Premium or MIP. 

You really don't need that LLC until you pay off the property and it's questionable if you need it then as long as you maintain your property and have correct insurance.Yes to wind insurance, not sure about hurricane.I use Foremost STR policy for one property.I am about to switch to USAA (retired Navy) for another because they quoted a policy that was 3k lower than what we have.

What is she doing now in terms of paying for housing? 

Reporting the proceeds you pay to seller on a 1099 sounds reasonable.

You let it slide, waive the late fee, and she pays by the 10th.

If you have a buyer's agent, you should have already signed a buyer's representation agreement and that fee/commission is disclosed in that document so you should very well know what that charge will be.If you were the seller and going to owner finance the property, what would you want to see from the buyer that tells you that they will be able to pay the mortgage moving forward. 

If it pays for itself, it provides you with a "free" place to live during the off-season.

Personally I wouldn't feel comfortable trying to wholesale a relatives $1M home knowing that I am breaking the law if I cross over into doing anything that can be considered representing them in the transaction, and knowing it will only be marketed to people who buy properties wholesale (typically investors who don't want to pay retail prices), instead of the majority of retail buyers active in the market who are typcially willing to pay more. 

https://treas-secure.state.mi....some things to keep in mind:-Non owner occupied properties pay 18 mils more in taxes in Michigan - Even with the SEV you should plan that the SEV will go up.