New Construction high density apartment cash on cash return

Hello everyone, this my official first post. Please take it easy on me. Here is the low down.

Location- Union County NJ

What- 1 acre lot for 1.2mm

Want- Build a high density 30 (1 bedroom w/study) unit apartment building with required parking on site . Architect confirmed this can be done with a 4 floor height variance. Each unit will rent for a conservative $1600 a month plus utils. 

Question- We are estimating approximately 2.8mm construction costs. Site is already leveled and irrigation taken care of. Will have outdoor, on grade parking- With a total of 4mm into the site and construction, how do I determine the cash on cash of the entire project? $600k down for the land and then 30% down for the remaining 2.8mm. Lets say its a 5% interest loan over 30 yrs. Is there a general percentage for , maintenance and management, vacancy rate (5%)which we can factor in to get the NOI? The taxes will be around 30k yr

I apologize if I left out any pertinent info required to do the math. 

Thanks in advance