I have done some preliminary research into these zipcodes and have demographic stats of the neighborhoods. 

Due diligence should include tax returns and personal financial statement on tenant, tax returns on the building and preliminary environmental assessment.

During this time run a title preliminary report to see if there arw any liens or judgments ties to the property, get pay off and reinstatement quotes so you can asses the deal and see what you are working with before negotiating a deal.

What you want from the Title company is a "Preliminary Title Report."

This is a basic preliminary analysis that I'm trying to drill down into.  

(A recorded trustee's deed (or similar alternative) confirming the amount paid by the grantee to trustee may be substituted for a settlement statement if a settlement statement was not provided to the purchaser at time of sale.)The preliminary title search or report must confirm that there are no existing liens on the subject property.The sources of funds for the purchase transaction are documented (such as bank statements, personal loan documents, or a HELOC on another property).If the source of funds used to acquire the property was an unsecured loan or a loan secured by an asset other than the subject property (such as a HELOC secured by another property), the settlement statement for the refinance transaction must reflect that all cash-out proceeds be used to pay off or pay down, as applicable, the loan used to purchase the property.

He stated that I would first have to make a preliminary offer to him for him to decide if it's worth talking about selling.

I would start shopping for a good Independent agent and get preliminary quotes.  

I'm trying to get some preliminary numbers to see if this is a realistic possibility.  

@Morgan Merritt MLS listings for investment properties usually include a breakdown of gross rental income, annual expenses, even cap rate right in the listing info, which should be enough to give you a snapshot of the (supposed) past performance of the property and run your own preliminary financial analysis.