I liked the tenant, school is starting back etc, I told them they could pay first month and security deposit and I would let them have the rest of August for free.

I would look FAR AND WIDE for someone to do an investment property HELOC -OR- go to a bunch of banks and CUs (including who you bank with now) to find someone to provide an unsecured (or secured if you have other collateral) LOC to get rid of the high int debt.

Renter's Insurance is a cheap date for the tenant; it protects their security deposit and assets. 

What I've seen is that when asked to provide an assurance that a loan wouldn't be called because of a due on sale clause being triggered, the lender customer service typically just outright says it's not allowed, or default to a "no", because they see it as a black and white question, and miss why the due on sale clause is actually written into the mortgage document to begin with.If one is transferring property title from personal name, a Grant/Warranty Deed would be drafted/recorded to transfer title.

I noticed that the previous owner let them pay half the security deposit and the other half later, which is a red flag.

It’s inexpensive to provide but can make a big impact.Comfortable Bedding: Investing in high-quality mattresses, pillows, and linens improves the guest experience and leads to better reviews, which can boost occupancy rates.Smart TV or Streaming Services: Offering Netflix, Hulu, or similar services is a low-cost way to enhance guest entertainment and stay competitive.Fully Stocked Kitchen: A well-equipped kitchen with basic appliances and utensils appeals to families and long-term guests, saving them money on dining out.Dedicated Workspace: If your property caters to remote workers, adding a small desk and ergonomic chair can set your listing apart.Outdoor Spaces: If your property allows, an outdoor seating area, fire pit, or hot tub can significantly increase your nightly rate and attract more bookings.Energy-Efficient Features: Guests appreciate eco-friendly options like LED lighting, smart thermostats, or solar panels, especially in eco-conscious markets.Keyless Entry: A smart lock is a relatively small investment but offers convenience and security, which many guests value.If you’re deciding on amenities to add, it’s always a good idea to research your local market.

Assuming plans are needed to secure a permit.

In short, securing an STR permit isn’t easy unless you fulfill all the township’s requirements

It isn't having paid off properties that offers security, there are still taxes, insurance, maintenance and management involved. 

End to end, I bought the land, secured permits, got the PPA and IA, SUP, and still own the project.