How do I make a simple report that will show me the percentage of plays by Category? I want to see if my formatting is delivering 15% Hot Current, 20% Medium Current and so on.

Create a new song report. Sort songs by Category. Put a check mark in the Sort 1 Heading print box.
Now, Click “Edit Track Fields”.  Do not add any fields and do not check the Print box for Notes or History.  Close the Edit Track Fields window.
Select all the categories to include in the report.
The default of 7 days is probably what you want to use, that will show you the total week percentages. If you want a report of Weekday-only category percentages, enter 5 days. Then, whenever you print the report change the start and end dates to “last week’s” Monday and Friday dates.
When you go to print, give it some time to do the calculations and begin printing.