I think your rents are optimistic and you will pay with higher vacancy and poorer tenant quality (trashed units) unless you are in a more desirable area.I think a bigger question for yourself is do you want to deal with the type of tenants that come with this property and this area?

Once the lease runs out, you can give an adequate notice and raise the rents.One thing to consider is how long typical vacancies are in your area and how much work the unit will need.

In the past 3 years I've had 100% occupancy and even with a couple of turnovers haven't had a month of vacancy.  

Also, under expenses, I'm not sure what to put as far as maintenance and vacancy.

Between mortgage, taxes, insurance, vacancy, and maintenance, it would seem difficult to achieve positive cash flow.

My first purchase in Hawaii in 1978 has experienced 6%+ annual rent growth and appreciation of 9%+ annually and not one day of unplanned vacancy. 

I have found that good tenants have brought my vacancy and expenses very low.

If your multi family is in a less desirable area expect vacancy, maintenance, theft and vandalism.  

That $3/mo is losing money in real life with repairs, vacancies, etc.

On a month-to-month rental agreement, the tenant can also legally leave at a bad time when it's hard to fill the vacancy.