I try to think of everything anyone would need to cook anything. 

Living in the Chicagoland area, multifamily units in Chicago proper are an investor's go-to but I don't necessarily want to deal with Chicago/Cook taxes and duplex/multifamily building stock is dramatically lower in the suburbs so might go single family home in DuPage or Will.

It is getting harder to find 1% rules in good neighborhoods but a lot of investors do very well with buying cash flowing C class rentals, having a property manager, and repeating.Welcome!

(ie class, crime, job market growth) I noticed this has been done for several other metro areas.

Nothing too fancy, just a basic 2 story 3 bed 2 bath home that would be built in a Class B or C neighborhood.

For all of the middle class people that you see staying home instead of going to the Smokies, there are people who might have gone to Europe that are staying closer instead.

I would recommend that you find a local property manager who deals in this size of asset classes, and talk to them about how you would turnover units at this scale. 90 units is no joke so I would leverage your property manager for their GCs or remodeling companies who can help you out with this.

Seems like B and A classes don't provide high cashflow after operating cost.  

@Michael DubovskyThere is no 'best area' to invest in.Each area is different and has their pros / cons.I think it is your job to identify what your 'CCC(Crystal Clear Criteria)'(Price of home, property type, asset class) before investors can suggest an area for you to invest in.

2) Search here on BP for Morris Invest - infamous for selling Class C/D properties as Class A/B.