You can never be too prepared. Maybe after years of teaching you can be prepared for all the questions you'll be asked, prepared for all the problems students are going to have.
In almost every class I have (at least) two levels of students and keeping track of where everyone is at all times is just another level of prep. Then you have all the assessments to be ready for - who has passed this NAB, where do I get extra revision stuff from (and solutions for them).
A student (or students) is (are) having trouble with a particular topic. Do I prepare more materials, search online, wait for a while and review it with the whole class, ask them to stay behind so I can discuss it with them? All of which you have to prepared for. Currently I'm finding the easiest thing is to try to prepare for everything and then you're prepared for nearly everything...
I'll keep you updated.