My team and I are in the Detroit, MI marketplace and it is the market we've picked.

My favorite use of PS is to dig into a property's mortgage, MLS listing status, BK, divorce, liens (especially liens) and forclosure status. 

Old homes have plaster, lath, knob and tube electric, 50 windows that are wood and half don't open, the list goes on and on (stone basements, structural issues), just don't buy old multifamily.

Anything less than that is a mediocre company with poor properties/listings, so we're targeting those STR homeowners.  

For closing costs is there a list I can find that defines the 4 different groups.

It is absolutely fine to accept multiple applications and pick the best one.

Rent prices right now have downward pressure, but that could simply be seasonality.One trend that is common when looking at good deals are houses that are listed with more bedrooms or bathrooms then what the city has listed. 

Too many to list Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

The best source may be to call active listings as well.

Good pick, I've seen a lot of success in Ohio.