This is such a difficult question to answer. It depends on how active they are, what material they are looking at, how big are the files they are looking at.
The place to start is probably to try and get an average idea of the size of a single page - a page may be material typed into Moodle, a PowerPoint presentation, a Word document - whatever but try and get an idea. You can then divide this into 10GB and then divide it by the number of students. This will then give you an idea if 10GB sounds reasonable. Many browsers give you information about this if you dig about.
Next you need to try and assess if 450MB is enough space to store all your material. This will be the total of all your files (Word, Powerpoint, pictures etc etc), or at least a good guess at it. Is there any limit of the database
size? A lot of stuff gets stored there too?
I hope this helps you....