Their combined monthly income is 3X my rental amount but the man's income is in cash (he is a car mechanic).

When the rental was published, they added a mechanical lock with the house keys inside.

@Fahima Hilal an architect usually only outlines mechanicals, plumbing & electrical on their blueprints.Your contracts should be creating appropriate drawings showing where their stuff would go and submit to city with their permit application.

Depends on the age of the building, mechanical systems, etc but good rule of thumb is 6 months of reserves liquid to feel safe

@Jake HughesCost segs can be an amazing tax deferral mechanism but they are not a one size fits all solution.  

But I'm not familiar if title could get clouded from another mechanism at the state DMV for instance Thank you for your response!

But larger repair items such as appliances and mechanical, plumbing, electrical, roof windows doors etc should still fall under the landlord's responsibility.

In your property folder I'd include a "Closing Folder" with your closing statement and original home inspection (all your major mechanical pictures and ages are there).

Are there separate mechanicals for each unit?

You have a mechanical skillset you are perfecting so you will always have your trade to barter for access.