converting duplex into 5-6 unit

[Duane Brown]

I am an engineer and young investor currently I have 4 doors in Trenton and Ewing NJ area, My question today is, I have a duplex, that is on the big lot, (10+ car parking lot) and I am working with an architect and the Zoning officer planning to add to 3 - 4 more units on this lot.(It has been already approved via township zoning officer .YAY!) Does anyone have any tips or suggestions for me during this process. As you know five unit building or more the valuation is based on the NOI. What should my main considerations be? Construction cost of course but.. Refinancing out? The amount of rent per unit? Expenses? TIME? Modular? The current duplex currently rents for $2000 a month, my goal is to get at least three units at $1000+ a unit, and have a NOI of at least 5k a month or $60,000 a year.

60k-15k (expense) = 45k NOI45k/.10 cap rate= valuation of 450K!

Am I missing anything here? Is a HML my best option to fund the deal?
Refinancing out….I purchased the property last year for 125k and have 90k debt on duplex.

Cash out refi would be 450k(ARV)- 90k(debt) =360k*.75(LTV)=270K

This seems like a no brainer if I can keep construction around 200K Attached is the sketch from the architect.

Any insight would be great! Happy investing guys!