Defending your personal investment is frowned upon appparently.

Because of that, I believe I can legally keep the entire security deposit.

People are getting poorer quicker and wages are not keeping pace with the cost of living.  

In addition, what do you do in the summer to keep your STR booked?

Personally, I'm not willing to deal with the headache of constant switching, especially since my market allows me to flip to STR to fill awkward gaps.

There are several components to keep in mind, none are too complicated.Provide a Purchase Option and a Lease Agreement as separate documents, if they dont pay rent, you can just show the lease agreement to the courts (without showing the Purchase Option and complicating the eviction).

It comes down to the landlord keeping good records and following the laws correctly. 

Should I keep negotiating it or this is a good deal?  

We would like to buy this home with the intent to keep the for 3 years at least.

Schlage lock and Wink Hubhttps://www.amazon.com/Schlage-Connect-Touchscreen...https://www.amazon.com/Wink-Easily-Control-Device-...FANTASTICWink hub makes your home a "Smart Home" and the Schlage lock allows you to personally enter codes.