I ran some numbers myself and although your repair and maintenance estimates are a bit low - I doubled them in my calcs - I also added the vacancy rate of 7% cause I always like be more conservative in my calculations - further more , to be sure its a good deal , you really should add the management fee cause otherwise you are making calculations based on you always managing the place yourself - ( which you may plan to do anyway ) however - I like to calculate what the cash flow would be if you had to walk away from the day to day operations and bring in manager   -  That being said - It looks like you are looking at roughly 934/ Mo in cashflow or $11,220 a year yielding you about 15.6% Cash on Cash return the fist year  - not a bad deal at all.

That averages to $19,600 per property as the target re-sale value.There will be closing costs to factor in on the re-sale (estimate another $15,000)Plan is to market them for a little over $1m (for 51 units plus a garage, that's damn good!!)

From what you say, the agent has a higher estimate of what the bid should be than you do in every case.  

Scott The Book on Flipping Houses, The Book on Estimating ReHab Costs http://www.biggerpockets.com/flippingbookYou might consider Niche or Specialized Housing like student housing.

Some people in my neightborhood got one contractor to throw that in for free.Everything above needs to be spelled out in the estimate they give you.

If my assumptions are correct, and some may not be, seeing as I am unsure as how to best estimate certain ratios, or percentages.

Next steps:-Do the research on market value, rehab, rents, etc - what resources can help channel my action here so I don't over or under estimate?

To get a rough estimate you can use something like rentometer.com to see if there is indeed any rental properties near by.

My estimate of its value: $300-350K based solely on listing prices in the area.

Scott The Book on Flipping Houses, The Book on Estimating ReHab Costs http://www.biggerpockets.com/flippingbookConsider checking out HUD homes for small multi's owner occupied gets first crack.