I am annoyed at the situation because it betrays a level of inattentiveness to the property they are being paid to manage.

I am filling out the warranty deed and was wondering if I can leave the Consideration part blank or do I need to fill it in with "for $10.00 paid and good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged".Thank you! 

It was difficult to verify income because of cash paid construction jobs, but previous landlord confirmed they never missed a payment.

Many online mentors from articles ,seminars, and podcasts have said to get up and start now.  

The owner was 80 years-old and had the property all paid off(dealing with a very motivated seller).

Appears in pretty good shape from an online search.  

I'd like to retire or maybe semi-retire in about 10 - 15 years.I've been going through the BiggerPockets webinars, and hitting every online resource I could find for the last 2 months.I've settled on trying to purchase a Multi-Family 5+ building on Chicago's SouthSide.

You ccan search online what the average price is for a repair - IE- thermocouple for water heater. etcI think Cozy is a good website for basic PM stuff.  

Would it be in my best interest to come under contract with a realtor that I have a rapport with and gets paid by the buyer/me? 

What seems to work the best is to use google spreadsheets with a bunch of paid extensions that can find duplicates, cross search between sheets, mail merge, etc.