Yup, parts of the Shedd are under construction. Not a highlight at the moment.
I'll weigh in on the pizza debate -- I live on the south side of town but I work on the north side, so I've tried them all! I like Gino's East and Giordano's, but Lou's is still the best for me. They have an amazing salad there, too, if you like having something with your pizza.
Your hotel is in a great location. I agree that the location is the Mag Mile, though you're pretty close to the Gold Coast. All the restaurants suggested have been good, but you might want to try the Grand Cafe Luxe on Michigan (at Ontario) if you're looking for additional alternatives. They do breakfast on the weekends, starting around 10am I think. Cafe Iberico is my favorite place in town. If you like tapas, it's amazing. We have a great Greek Town also, if that appeals to you. Tea at the Drake is fun, and, if the weather is nice, there are some nice restaurants along the river.
Regarding the hotdogs, the only place that comes to mind is Portillos. It's fast food, but the hotdogs are good. You're really not going to find many street vendors -- I've lived here all my life (except for college/grad school) and have never eaten from a street cart. I just asked my parents, who can draw on 55 years and 64 years of Chicago living respectively, and they couldn't come up with a single hot dog place except the ball parks! Find a place with a Vienna hot dogs sign and dig in.
As for museums, I think the Art Institute is a jewel. I'm not a big fan of the Field Museum. The Grant Park/Millenium Park/Museum Campus area along the lake is lovely. If the Buckingham Fountain rehab is done, that's a great thing to see. The best experience in town is the Architecture Foundation boat trip that others have mentioned, so be sure to squeeze that in to your itinerary.
Have a great trip!
