Market for the same size in my neighborhood is around $650-750, but I charge $900-1000.

Should all units be the same size or should they be different?

From all the podcasts and all the reading I have done here, I just dont see how people are truly cashing in as small to mid size REIs. $100/door would put me at 30 units a month just to cover my bills.

With a good size family to support I'm going to have to start small and smart.

Eventually, I would like to have a substantial RE portfolio specializing in small to medium size apartments in urban areas and more specifically surrounding prominent universities. 

There's a slew of other factors that can impact your rental such as the demographics, property type, size, age, etc. 

What are the sizes of the units?

If it is the first then it would seem you have a case to challenge their requirement, since as noted on the chart there isn't a requirement for a PE signature on building plans for that specific project. 

Average loan size was $248,285 and average LTV 123%.

If the garage space is 22' x 10" (typical size), this would be about $38/s.f.