Marese,
First, Welcome to the ACA Forums! However, be forewarned that touring can be a very addictive hobby.
Second, you might consider renaming your user id so your email is not displayed. Spam bots can harvest it and then you will see more junk mail. People can still email you if you list your email under your profile.
Now on to your question. A mid-August departure from Chicago is fine. In order to determine when you should leave NYC, I would suggest you first do a few multi-day (3-4 day) loaded as if you were on the "real" tour to determine YOUR average miles per day you are comfortable doing. Knock off about 10% for rest days, weather or mechanical delays, etc. to determine your overall average miles per day. Riding a touring bike is not the same as racing. I have done both. Touring miles are a lot less because you are carrying a lot more weight and the bike itself probably weighs more. Do not assume that since you can do 75 miles on a racing bike that you can do 75 miles easily on a touring bike. As a reference, I would say the "average" people tend to tour is about 55 miles per day with the ranging being from 50-60 overall. Sure you have people who average 30 and others who average 110+. Those are the outliers.
Once you know your overall average per day, do the math and determine how many days you will take to get from NYC to Chicago. Since the Chicago-NYC route has a couple of options, I won't go into them all. Say your overall average turns out to be 50 miles per day and the route you choose is 1,100 miles. It would take approximately 22 days +/- a day or two to ride from NYC to Chicago. So if you wanted to leave Chicago on August 15, you would need to leave NYC approximately July 25 or so. Obviously, if you have higher overall miles per day, the leave date can be later and vice versa.
As far as the other info, check out the journals over at Cycle Blaze or CrazyGuyonaBike. A word of caution, try not to plan too much. Knowing exactly what is ahead can really ruin the sense of discovery which is what makes touring so great. If you are fairly in shape, know who to do basic bike maintenance like change a flat, and have realistic daily mileage goals, you will be fine. The ACA maps are fantastic. When used in conjunction with the app or a GPS, you should be fine.
Tailwinds, John