Most of this information you could easily find through Google.
Clayton campus is far larger than the Caulfield campus, with many more units, students and other offerings. Arguably, the latter has a better location, with better quality food, nearer to transport, et cetera.
Some course - particularly double degrees - have units located in both campuses. There is a shuttle bus that runs between the two, and is quite convenient. I believe that the majority of Arts units are actually in Clayton, and so if you pursue Arts/Bus (for example) many of your Arts units could be in Clayton.
Everything you might be wanting to know about a particular course can by found in its Handbook entry.
Here is the entry for Arts/SecEd. Looking at the
admission requirements, it is apparent that Units 1/2 OR 3/4 of any Maths (apart from Foundations) is sufficient.