K.T.
I ditto the previous posts. Definately stay Gold Coast . There are some great hotels that face the lake. And there are some boutique hotels (very nice) Look online, September (after Labor Day) I would assume would have good bargins. Architechtural tour...must. The buildings, river and lake are like nowhere else. My girlfriend took her teen daugthers (15 & 17), Mom (65+) and herself (45+) on a Segway tour through Millinium Park and south on LSD (Lake Shore Drive) had a blast and said it was easy even for her mom, except she had on heeled boots....she recommends flats.
You can shop of course on Michigan Ave and then go for afternoon tea at the Drake Hotel. Or ride the "L". That is the Elevated train that goes around the loop (dowtown). These are all very genuine Chicago things. All of the museums are great....but you will never get through all of them in a weekend, you would really need to devote an entire day to each one.
There are tons of different neighborhoods and the food....the food....take your pick! You will find the people friendly and hopefully the weather will be good!