For a new show, you can estimate how many panels it can support from the number of people attending (and that's distinct people, not number of gate admissions - and estimate conservatively).  It takes more people per panel for larger cons.  A rough formula for maximum number of panels/tables is:
 
For a new show, you can estimate how many panels it can support from the number of people attending (and that's distinct people, not number of gate admissions - and estimate conservatively).  It takes more people per panel for larger cons.  A rough formula for maximum number of panels/tables is: