It's done well enough to keep the lights on with a modest profit, but definitely could do a lot better with more of that experienced property manager's "secret sauce".

You can also do a skiptrace to find their address and or phone number as well.

Some conventional programs go up to 50% DTI as well. 

A super ball number to get you going would be at least $190/SF-$220/sf ish... to figure out square footage it's probably best to connect with a Chicago architect like @Samuel Pavlovcik or @Prashanth Mahakali both can talk through the zoning and plan development process.

Wealthy 2nd homeowners looking for someone to manage their home 11 months out of the year will gladly pay higher fees if you can demonstrate you’ll properly take care of their home and perform well.

Also, you're able to keep the loan current if you're planning to keep the seller's name on the mortgage until it's paid off.

@Srinath GopinathanI don't have an exact answer for you - but would guess that it is because the the covenants and bylaws spell out what the separations are between what the HOA is responsible for, as well as what the condo owner is responsible for.  

In addition - checking account statements showing deposit income going back X number of months would also do that as well.  

I plan on building a duplex (so 2 kitchens and 2 living rooms).

I know them well.