My prof has 23 different reading assignments, with 3 pages from here and 6 pages from there. Do I really need to enter each one as a separate assignment?

No. You have a few options for how you can enter that.

1. Use the Weekly Assignment category option, and the planner will schedule weekly time each week, which you can just use for reading for that class.

2. You can keep using the Reading category, but just total up the pages to read before the test, and enter that as one reading assignment. The planner will break it down into 2-hour reading portions and schedule it into the weeks before the test. Then when you are taking time to do, say, History reading, you can check your notes for the exact pages you need to read.