When will we know what books we need to buy and will we have enough time to try to buy online to save money?
They may actually already be posted online. I think I saw a link to that somewhere.
Will we really save that much buying online?
It's not like there is a huge market for these books out there.
Unless they've changed since previous years, you won't know which books you need until a few days before classes start. It depends on which section you get assigned to, because that determines which professors you'll have and they're the ones who assign which books you need.
However, I did have one friend who was fanatic about buying all her books used from places like half.com and so on, and I think she seriously managed to save about $400. I spent about $800-850 on my books first semester, but I only managed to get one of them used, I think. So that's about as bad as it gets (of course, that's not counting what you'll spend on study aids... they're worse than crack.)