The 50% rule and our first two-family rental property

[Matthew A.]

Hello everyone, this is my very first post. I am pretty well educated on a lot of the terms and about REI in general, but I am still confused about the 50% rule and some of the math. Since I over analyze everything, I have a feeling when I do get my first property it will be a good one since my math brain won't allow me to screw up :).

Here goes. 

Me and my girlfriend are looking at buying our first owner-occupied multifamily. To be precise, a two family in the northeast. 

I am going to make a lot of assumptions on numbers which is based off of what I calculated so bear with me. 

The house we are looking at is listed for $85,000

We are going to do the FHA 203(K) full renovation loan considering this place needs some work.

I don't want to spend more than 75k on the entire reno. I have a lot of line items, so just believe me when I say that's about how much it will cost, and forgot all the details that go into it. 

$160,000 total purchase+reno budget

We are putting down the minimum require 3.5% @ $5,600 (30 year fixed @ 4.5%)

Closing Costs might be 3% @ $4,800 (not always 100% about these prices)

My friend who is the realtor and licensed contractor will not be taking any commission from me. 

OK number crunch time:

My long time friend and "realtor" has flipped and has many rental properties so I trust him.  The property is located on a college and he believes it could pull $600 a student per room. It's a 2 unit (2/1 and 3/1) so essentially grossing $3,000 a month. 

$160,000 loan

$5,600 down-payment

$4,800 closing

PIMI: $770 (Principle+Interest) $133 (Insurance) $440 (Property Taxes EXTREMELY HIGH IN CT) and $96(Mortgage Insurance) = $1,440 a month. 

NOW! here is where I confuse myself and can't seem to have a great grasp on the numbers assuming the 50% rule. 

Is the $3,000 x 50% rule assuming maintenance, vacany, CapEX and PIMI or everything minus the PIMI. 

Would I be right to assume that I would be netting only $60 a month according to the 50% rule, or would I be netting the $3,000 - $1,440 = $1560*.50 which comes to $780.

Is it...

$60 

or 

$780 I can expect (less any other unknowns or fees associated with the place)

Thanks! and I'm excited to start talking on BP more often, and hopefully can impress a few of you down the road on some of my future potential deals!

-Matt