In my opinion this sounds like a substantial investment, and there are plenty of solid multi-family renters in the following markets:DearbornDearborn Heights Melvindale Westland& other cities immediately North, East, or West, of Detroit You're spot on about renters paying less for a duplex over a SFH but as you progress in the multi-family market you'll notice the differences aren't much if you choose the right property, construction finishes/overhead, tenant screening processes. 

I will keep you all posted on my progress if we get the deal under contract.

Congrats on all your progress to date and congrats on the upcoming addition to the family!

It feels like the natural progression to move into real estate investing in a bigger way now.

IE never gentrify and values never changed from the peak of the 80s.. its picking those path of progress that is were the real money Is made in real estate you get your cash flow and MASSIVE appreciation . or you need 100s of doors if your only going to count on 100 or 200 a month for cash flow for decades.. 

Keep us posted on the project as it progresses.

(the order of some things may change as work progresses - this always happens) BUT you want a plan for the rehab.#2 You want the contractor to be efficient. 

@Paul Caporali remember this game is slow and steady.As time progresses you will find other opportunities to help you towards your next if you work at it.Keep building/creating equity you can use, keep networking so you can create relationships for the future(partnerships etc).

Any thoughts on what to watch out for if I do progress to an agreement with him? 

Keep us posted here on your progress!