Not sure if it's cheaper to get tickets here or when you are there but I bought mine before we went. Having said that,most people were paying on the day.
We drove to the Space Center from Orlando and its easy. From the I4 take the 528 to the center. It's well sign posted.
Once there ,there are plenty of exhibits to look at.
The bus tour takes you around the center and you get off at various points and have a look around then get on the bus and move to the next stop and so on.
The nearest you get to the shuttle ( which was on the launch pad when we were there 2 weeks ago, but they might be taking it off soon) is about a mile or so away but you can see it ok.