One of the best ways to get involved in this arena is to hire a paid coach.

Are you able to do renovations yourself or are you going to hire this work out?

If there are qualified to do the work, hire them...they will need to pull permits for some work, and likely sub out skilled trades like plumbing, HVAC and electric...work on a draw schedule...only pay for work completed once it's verified...and have an agreement in place before you start any work.

With how long they lived there and their age, I would ask them if they have family to help them move their treasures, and if not, you hire insured professionals to do it. 

Would you consider hiring someone to manage the guest house for you so you could have more free time to do other things?

If you just hire the cheapest or first PMC you speak with and it turns into a bad experience, please don’t assume ALL PMC’s are bad and start trashing PMC’s in general.

Since I work with realtors so much, I bet I could do the listing myself, but still will probably hire a listing agent. 

Then just hire a crew to maintain it.

In Texas if you act as a property manager for hire and are not a licensed agent you are not able to charge separate lease fees.

I personally have never been involved in the rezoning of a building in Chicago.However, a Google search helped me find this City of Chicago website about the process of amending the zoning of a building in Chicago: City of Chicago :: Zoning AmendmentFrankly it doesn't look like there is a fast way to complete the process before purchasing the subject property.It looks like you will need the approval of the City Council of Chicago and therefore it might be a good idea at some point to reach out to the Alderman for support.More specifically, it will be a good idea to hire an attorney to represent you who has experience dealing with the Chicago zoning board and local politicians.Therefore, a price reduction could/should be requested.Good luck