@Account Closed
I am as much a newbie as you are (if not more so) but I'll give it a shot (any pros that want to correct me please feel free). Based on a cap rate of 12% (ask him for the exact numbers he is using to come up with that), the NOI is approximately $145,000. Cap Rate = NOI / Market value ($1.2m). NOI (net operating income) = revenue - expenses (not including taxes and mortgage). So I arrive at a rough NOI of $145,000 since 145,000 / 1.2m = 12%.
The income range you provided is, I presume, the difference between all units with a single occupant at $875 per month ($13,125 for 15 units) up to an average of 4 occupants per unit at $1415 per month ($21,225 for 15 units). I would ask for a "rent roll" which is a list of the current rent being charged for each unit. That will tell you 1) what the "real" mix is based on current occupancy and 2) what the current vacancies are and 3) what your actual income is likely to be.
If we assume, for the sake of argument, that the "average" rent is $1,100 per month (2-3 people per unit), actual income would be $16,500 minus vacancy rate of let's say 3%, which would put you around $16,000 per month, or $192,000 income per year.
If you subtract the NOI from gross income (192,000-145,000) you have expenses at $47,000 per year before mortgage and taxes.
By jumping over to the Zillow mortgage calculator and plugging in $1.2m price with $350k down on a 30 year mortgage at 5% interest, the monthly payment (with taxes and insurance) is estimated at $5,830, or $69,960 per year. I have no idea if those terms work for your seller, so your mileage may vary, but I'll use those numbers for the next calculations.
Now, if you subtract your mortgage payments from your NOI, you have 145,000 - 69,960 = $75,040 in net annual cash flow, or a 21% annual return. Your down payment could be paid back in full in about 5-6 years or you could pay it back as a percentage of net cash flow over a longer term depending on where you get it from and how much you want to keep for yourself in the early years.
Now, two things to keep in mind...
First, I may have royally screwed something up in my calculations. I have not actually done any of this with real money. I did it all by hand based on memory and I certainly may have gotten something wrong or left something out. I've been studying the analysis process and the main reason I am even replying to your post is because I enjoy the practice (and hope I can help you out in the process).
Second, there are a number of assumptions that you really, really, really need to verify. I may have been too optimistic in my assumptions. You probably want to see some tax returns, leases, etc... to make sure everything is on the up and up, especially on the expense side.
Bottom line, consider this as nothing more than an effort to help you think this thing through. I hope someone with more experience will review my post and confirm or deny my math, and I hope this helps to at least get you on the right track.