You are using so many assumptions that it's hard to offer any legitimate advice. I will say this - for $25,000 per unit (i.e. $400,000 total), someone could buy a 16-unit building for $5.46M and renovate to be all in for under $6M with finishing surfaces close to what you are proposing for your new construction.
Now, if this allows them to achieve the same rents as what you are proposing, then you can clearly see the problem - their valuation, all things equal will be same as yours. With a lot less risk and a much lower basis.
But, let's say they will not be able to hit your numbers. Let's say they do 50% and add about $70,000 to their income, for a total of $320,000. At 3.66 cap their valuation will still be almost $7M: $320,000x.8/cap rate of 3.66
Brand new product is special, no question. But, where is that line in the sand? How much will someone pay extr4a for something that's new? Specifically, on a risk-adjusted basis...