Subsequently I was a Series 7 stock broker on Wall St. for almost a decade.

If it was, then why isn’t the first series of payments 100% interest?  

For that you might want to read our series about “How to Screen a PMC Better than a Tenant”: https://www.biggerpockets.com/member-blogs/3094/91877-how-to-screen-a-pmc-better-than-a-tenant-part-1-services-and-processes

Here's an example of a solid door for the front, with some windows:http://www.lowes.com/pd_420697-56870-123537_429485...http://www.homedepot.com/p/Clopay-Value-Series-8-f...And an example of one with a pass-through door, which is what I'd do for the back:http://www.portesmg.com/portepieton4.pngAnyway, just a thought.  

I use the Schlage Camelot series, I prefer the manual deadbolt (no motor to wear out).

It blew my mind the first time someone driving a 7 series argued with me about a $20 tire repair.

It took @Charlie Hampton more than a year to get rid of a guy who was squatting in a old shed in a property partly because he initiated "eviction" procedures, which gave the squatter access to a whole series of rights he savvily exploited. https://www.biggerpockets.com/forums/52/topics/110018-update-on-my-squatter?

For a few months I've been learning about how to use my unused income from a full-time job to invest in real estate and have been reading lots of books like Hold: How to Find, Buy and Rent Houses for Wealth, Brandon Turner's books, E-Myth Real Estate Investor, the Rich Dad Poor Dad series, and listening to the BiggerPockets podcasts. 

If you were to ever end up in court, you just need to prove that you had a written contract that you both agreed to - if it's for a year or longer, and that money passed hands to clinch the deal.  

They wanted to get out of their lease and so they papered me with a whole series of made up claims about maintenance, filing these with the Landlord and Tenant Board here in Ontario.