Lots of flips in that area too.I think price range is also a consideration.  

A good standard is around 8% (roughly one month vacant/year), but in super hot neighborhoods it will be lower, and in lower-demand neighborhoods it will be considerably higher. 

I want to build at least 3 stories high, how do I know the height limit that I am allowed to build in a residential area?

Running a split down a driveway and having a 12-16 inch height differential.

If you have children and you're looking to be in a nice suburb with good schools and nice single family homes, Schaumburg, Arlington Heights, and Libertyville would be great places to look.

Factors for consideration: I have 2 young children in car seats and that is pretty cramped in the fusion.

I choose to look at it as an added bonus that a landlord gets the opportunity to pick and choose his customer with a considerable amount of detail and to his/her benefit :)

You could also pay something similar to what this condo costs say right off of Good Hope Rd in Anacostia and get considerably higher upside on your appreciation than the condo you describe, but possibly with a higher risk tenant.

This has to do with privacy consideration, size of family, etc.  

Also, limit the  opportunity where someone can can fill in data in areas like Other Contingencies or Other Considerations.