With current interest rates, and they are at least 1% higher with potentially additional points for non owner occupied property, it is hard to find properties that will allow for positive cash flow after paying the mortgage, if you are looking for money for the down payment from a private lender, those are normally at higher than market and I am not sure it would be possible to pay it off.... please remember you need to take into account that you may not have a tenant for a certain amount of time, a tenant may stop paying rent, or you will have a big ticket item to fix, so I would wait if I were you and save to have enough for the down payment and closing costs and perhaps some money set aside for repairs. you also want to make sure that you have your own emergency fund outside of the money needed for the investment property because life happens ....

When you move out you begin to experience POSITIVE CASH FLOW in which your tenants help you buy the property.....where eventually you own it out right, and now it becomes like a pension..........Predictable and Sustainable income for life.   

Don't make your life more complicated than it has to be.

I will give you my real life example.

It frees you up to focus on living your life and acquiring more property.

I've been a real estate investor my entire life, doing my first deal as a senior in high school ($5,000 mobile home).

But I strongly urge anyone to always get Aldermanic support before proceeding because it makes life--and the entire project / process--a whole lot easier. :)IN SUM: Based on what you've shared, it sounds like you won't need to rezone if you just want to build a duplex.

Was truly one of the best financial decisions of my life. 

Search the BP for ADU appraisals to encounter numerous examples.

Fro the biggest reason, as you said, you own the home for the Best, First years of its life.