We've collected all that data on the size and price of the other duplexes on the street, which is good to keep records of. 

The book shows you how to develop Momentum Charts on Existing Home Sales, Building Permits, NOD, Foreclosure Sales, and interest rates.It took me several days geeking out and collecting the data, but now I just maintain the data sets and watch for patterns.

A good/knowledgable insurance agent is invaluable in the RE business.

Numbers look good.Just beware there is a wide variance in values from neighborhood to neighborhood in Joliet.  

Whether or not you can borrow cash to do the rehab, you may be able to recoup all of it or even more by refinancing after it's complete.Adding $925 in rents would add about 90-100K in value where I invest (maybe more maybe less in your area).  

Well I figured that that city is the only one that reports the information on number of rooms so because the data wasn't there for the other cities it was assumed those cities have houses with 0 bedrooms.

Though they appreciate their sale price increasing should they sell, they have to pay property tax that is commensurate with increases in value - so that if they don't sell, they feel like they are incurring a net loss by the appearance of big rehabbed houses on the block.

Ask the realtor for the past 2-3 years of operational finances  ... s/he will either try to intimidate you away from wanting/needing them - in which case, walk away - or will provide you with a set of rosy, half-fabricated numbers {accept these with scepticism ... if you get in the territory of a deal, you will ask for corroborating information from his/her accountant or tax returns}.Once you have the financial data, take a run at analysing it, then bring it here for folks to review and assist you with coaxing the {likely} truth from the numbers.

I am not sure if other states have something similar.Like @Nazz Wang @Cameron Palmer mentioned check the county historical data from the tax collector website to get the best idea.

And I'd bet less than 1% actually look at any demographic or economic data with the exception of the latest "Best Places to Live" article on Yahoo's homepage.Buying rentals here in California, SoCal specifically, works very well.