It will be much easier to do what you are asking if the property is owned free and clear, in which case you need to work with an attorney/title company to draw up the promissory note, deed of trust, etc. and then you could "wrap" a new note around the first note from you to the retail buyer.

The addition adds 1 bed, 1 bath, and a den (plan to knock a wall out to open up the living room that separates the den currently).

Details:Purchase price $69,000, 2.2k seller credit towards closing costsOne 2-bed 1-bath unit and One 1-bed 1-bath unit, shared basement. 

I just don't want to pay full retail and pay more than I should off the MLS because a good deal now will help me in the future with more equity and everything else.

From financing office buildings, office/retail condo projects, office parks, a residential subdivision, etc.

Of course we will do retail and we still invest ourselves, but we are there to help.

Make sure the buyers agent knows the purpose of your purchase, you can't buy retail.

Crowdnetic is a company that tracks crowdfunding and their quarterly report shows real estate leading by 3x over the next closest industry (retail).The marketplaces in the industry leading the charge in real estate are Fundrise, Realty Mogul, Patch of Land, RealCrowd, iFunding.

For Example a 1200 sq ft 3 bed home with neutral decor will rent for x amount of dollars.After you have figured out the rent and the product you want, factor in the 50% rule and then set the auto MLS search parameters for a low enough price point that it cash flows.

(i.e SFR, Multi-unit Properties, Fix and Flips, Retail commercial, and Construction.)