How much reading is appropriate to give to students?
It really depends on the focus of the class, and what other homework you are giving students.

Certain classes are expected to have more reading.  Societal and philosophical theory fields are heavy on reading, as are (obviously) literature classes. 

Remember, different students will read at different rates, and the more you cover the less detail you can cover.  It's sometimes better to go into deeper depth than to cover more for both these reasons.

It is important you disclose the reading to students as early as possible, preferably before they apply for your class.  At the very least all major reading assignments longer than a few pages should be disclosed on the first day of class.  This gives students that need to time to read ahead.