So the optimal income path from an investment perspective is, what sort of a job will get you into the highest possible pay early on for the least amount of education or certification or credentialing investment? 

People fake them all the time or just print certificates off a website.

I was set to close on my 2 flat last month but the closing has been push indefinitely because of the zoning certificate. 

What are the codes and certifications needed to comply?

STR restricted, occupancy tax, occupancy certificate, etc.

It's a little late in the game, but get what's called an Estoppel Certificate from both Seller & Tenant.

My younger self would be driving Amazon by day at $25/hour and taking online accelerated courses for business administration BA and MBA, and get certifications in project management like SAFe Advanced Scrum Master or Certified Scrum Product Owner. 

The Certificate of Insurance must be updated regularly.

Prior to closing you need to have an estoppel certificate stating rents and verifying terms of the lease, security deposits and any oral agreements.

One of the biggest misconceptions I do my best to help our fellow veteran brothers and sisters understand is that you can use your Certificate of Eligibility (COE) more than once.