Get an estimate on the engineering service.  

Few days after closing, visited property with contractor to get estimate to address some of the items that came up on inspection report. 

The estimate can be off which would sway things. 

This is what the owner provided as a P/L, but they are all just estimates, as neither has kept updated books.

Does anyone have a ballpark estimate of the cost to build a new side-by-side duplex in duplex which is 3–4 bedrooms, 2 baths per side with each side being approximately 1,500 square feet per side with a 1 car garage and a basement?

We invest in areas that without knowing the areas you can be in a war zone or a great area in the matter of a dozen blocks - investing remotely will never get you that intel.Another pitfall is the reno budget (under estimate), the time line and carrying costs (under estimate) and the ARV (usually over inflated). 

One piece of advice: really get to know the sub-markets (block by block in some areas) and run conservative rental estimates so you don’t get surprised after closing.

HostfullyAirbnb ManagerAirbtics – Strong for real-time pricing insights, ROI estimates, and performance breakdowns by bedroom count or location.

Using my best estimates, the property would cash flow as a LTR but I'm looking for strategies that can optimize this investment.

The softer resale market needs to be a factor in your decision making process and never try to force a deal to work by shaving costs off your reno estimates or hoping for a bigger sales price . . . never works out