The unit is currently zoned under multifamily-residential (2-4 units) and the City is planning re-zone the parcel into Commercial Office in 2019 (Up to 3 Commercial Offices).

There's commercial construction wherever you go and typically my cheap properties cost nearly $200k to get into. 

I would definitely never give them access to the property before receiving full payment.

My agent gets to make money and I/referrals get better access to more and more inventory.

What are the best resources to use while learning about commercial real estate investing (specifically large multi-family)?

But if you go to an owner you must find a way to provide value to make your proposal more attractive then someone's else.Know that anything over 4 units = commercial... different rules and different buyers.

What type of investing are you looking to do, buy and hold, flips, Commercial, or some kind of combo?

You may be able to get a commercial apartment loan with 20% down closer to 5%. 

I have a SFR that I want to convert to 3 or four rental units, I am confused by the IRC, definitions on duplex and townhomes, has anybody converted a big house into more than two units before, two stories, what is the big deal.mainly because of the commercial rezoning requirements and fire coder requirements (sprinkler systems) on new construction

Sell your home to access the equity if you can not refinance or get a HELOC to pull the equity.