First, let's discard some of your false remarks. One, you are young. Two, your time at Chicago is excellent for a first marathon. :-)
Now for what you want to hear.
1. Do run Columbus on 10/21. I know there are far more qualified advisors who will tell you to recover one day for each mile run, so that you should take 26.2 days off before getting back to serious training or racing. My own experience in running two marathons in the past year within 2 weeks of another marathon is that the second marathon is always less pleasant than the first but my times are better. If you have the same experience, then you may be in some pain during your final 10k at Columbus, but at least you will be running through this pain at a faster rate than you did in Chicago! :-)
2. My favorite recovery run is the 10k. Granted, I'm an old, slow guy. But if you do the same method, then run a 10k each day, starting today. It doesn't matter if you have to limp the 10k. What is important is that each day you improve, until you feel that you can run the 10k as fast and easily as you could before your first marathon. At that point, switch to your regular marathon training. I'll offer you my plan for my best marathon yet (NJ Shore): Sat, rest; Sun-Tue, 10m each; Wed, 18m; Thur-Fri, 4m each; Sat, rest; Sun, 26.2m PR.
You will get a lot of alternative advice here from very fast and very experienced runners. Use your judgment as to whatt will work best for you in the next two weeks.
Stay healthy, of course.
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