You’ll find that this forum and the people who frequent it will be a never ending source of info. to speak to your question of where to begin, depends on where you want to go. 

Best source (in markets that have no rent control) is either a realtor that deals with investors or a property manager.  

I don't understand why people keep boasting about total door count when they aren't sole owners.

The storage unit next to the garage will also get a face lift and be turned into a workshop/studio to provide a third source of income from the property.

Multiple income sources in a single purchase.

I like to look at properties not solely from the cash flow and return on investment, but also from the collection and quality standpoint.

I have scouted several possibilities but wanted some advice on how to source a duplex in this area. 

It can be exhausting trying to get this information yourself via the internet when so many "sources of information" offer conflicting reports or just blatantly try to push you through some sales funnel without bothering (or caring) to address your actual concerns. 

That is my main source of marketing and it works well for me.

Then you will have an the square footage you need, and a floor plan to use as disclosure of source.