What is the age of the building and were there any proposed or confirmed assessments by the HOA?

It will confirm  rent, security, and any other agreements whether written or verbal. 

I've got a Real Estate Agent, well a couple, I've got a project manager/Designer pretty lined up.

50% rule for the most part is designed to be taxes, insurance, maintenance, management, capex, vacancy, etc. 

If it's in the CBD it likely is allowed, but otherwise it probably isn't unless it has a commercial designation. 

Let's say that due to your dad's health they give you a note for 5 yrs. so in five years, the note is due.I can see a situation were note can be called, by design.

Today as I called to confirm the appointment, (he wouldn't respond to my partner) it seems like the property manager has many excuses to why we may not be able to get into all of the units tomorrow.

We love the layout and future design vision of the house. 

A few things I would have questions on/confirm before pulling the trigger. 

There is no deed recorded for the property and it is designated as "Unknown" and none has paid taxes during the 50 years.