It sounds more like you have created a junior accessory dwelling unit which is a bit different than an accessory dwelling unit in the terms of size, juniors are no larger than 500 sq feet and is created using an existing bedroom.

Current w2 income covers expenses, child support, etc, but leave only a small amount for savings so financing all of this will take some thought.My challenge is that I need to get 1 more bedroom in the mix with 2 sons growing and needing their space.My home is in the very narrow part of the city where accessory dwelling units are allowed and I have enough land to do it.

I'm in the process now of looking into Accessory dwelling units to maximize the duplex and still occupy. 

Also, owners have nice vehicles and spend extra on them like new chrome rims, fully tinted windows, and other dumb accessory stuff.

The backyard has a good space and I intended to put a tiny home / ADU (Accessory dwelling unit) in the back yard.

About 3 months ago, we decided to invest in a house (with rental accessory apartment) in an area where 3 of our kids go to college. 

Mac Dade Blvd and Chester Pike were never great, but now you've got tattoo parlors (nothing wrong with tattoos) and vape shops on these roads and many of the duplexes are near these locations.  

There are never enough clean rentals in the area, and you can also build an Accessory Dwelling Unit on almost any lot which will also provide you with additional income.

To subdivide down to the minimum 1.5 acres or keep it to 3-5 acre properties and go with a higher end single family builds with detached garage above accessory dwellings.

Also, I am wondering why, assuming you will live in one half of the Duplex, if you considered getting an Accessory License to do an STR (vacation rental).