Lots of good ideas and options for you so far. I would also suggest staying in the River North neighborhood or near Wacker Drive or Michigan Ave/State St in the Loop (much of the Loop is not as dead in the evening as people make it out to be). These areas offer easy access to the L, lots of dining options and are convenient to much of what you will be seeing and doing.
Walk around the Gold Coast neighborhood if you like architecture and seeing how the 1% live(d). Other fun neighborhoods are Old Town, Bucktown, Wicker Park, Lincoln Park, Lincoln Square, Hyde Park and the West Loop. You won't be able to hit them all so look into them and see which ones might interest you. There are of course, MANY others but those are generally the most popular. All are safe.
The Chicago Architecture Center on East Wacker Drive is a must and highly recommended. If you have an interest in architecture, they will fill it. But it is very accessible to non-architecture nerds too. And there are two great Jeanne Gang designed towers just nearby - two of the most interesting skyscrapers in Chicago in years.
For Oak Park, a car is not necessary to see the main Wright sites: his Home & Studio, Unity Temple and some of his best houses in the surrounding neighborhood. As someone mentioned, they are all a short walk from the L stations on the Green Line (Oak Park Ave or Harlem). The Hemingway Birthplace is also on Oak Park Ave if the recent PBS series interested you. There is only one hotel currently in Oak Park - the Carleton and it does have parking if you want a car to explore more to see other Wright Houses or suburbs like Berwyn or River Forest. But unless you are really committed to it, I would just use the L and your feet.
Chicago is arguably one of the best cities in the world for food. It certainly has some of the best Mexican food outside of Mexico and LOTs of "ethnic" food as it is one of the most culturally diverse cities. The challenge for you is finding places convenient for you that have some authenticity (there is some to be found in the Loop and River North - but the best are in the neighborhoods). And make sure to check websites vs a guidebook as many places might not have survived.
There is no telling what the scene will be in September. Things should be open and relatively back to normal - but not all restaurants will have survived and many are struggling to get re-staffed. By then things should have settled down, but no guidebook will be current. But one can give you a sense of where you want to go and use the internet to get more details.
