Do we need to rent a car in Omaha? Or is it possible to walk or Uber reasonably to most attractions?
If you're staying downtown and everything you want to see is downtown, you can easily Uber/walk. I'd try and stay somewhere near the Old Market.
If you want to go outside of Omaha or further west in Omaha, you'll want a car as public transportation is virtually nonexistent and Uber round trip will cost more than a rental for that day.