I'm dealing with three challenges: 1) roach residue in the kitchen cabinets 2) floor under the carpet is kinda gross 3) still not the best smell in the unitI contacted a company about what they would do and they wanted $150 for just an inspection and estimated treating the place (cleaning all surfaces, ozone machine, etc.) would cost thousands. 

Achieve your short-term goals that will produce proceeds and resources that will, 2.

If that unit is vacant turn on the ozone maker and walk away for a LONG time,,,like days or a week. 

His reasoning was to achieve early retirement.

Certainly if a unit is vacant you should be able to enter.

The third unit I called today and they said they will have it Monday, furthermore, they agreed to pay the late fee of $50.

If you are pursuing a residential (1-4 unit) or small commercial (5-8 unit), I would stick to the standard agreement, perhaps with my own schedule on a larger property.

Best of luck on your journey to becoming a professional engineer and achieving your real estate goals.

Consider that the other unit is paying or close to paying the debt service and you have little to no house payment. 

And, just to be clear, I'm not trying to setup an additional unit--I am just trying to accomplish receiving mail to '123 Main St