Most web comics are not drawn by geniuses, but I think the number of monkey's you'd need would depend on the quality of the comic and the frequency at which you expect to update it.
For a great comic that updates 5 times a week, I think you'd need 307 monkeys.
For the average comic, the number drops to around 10.
For this comic, I'd say 3.
All of those figures assume these are new monkeys and not the same monkeys that were trained to work on Shakespeare. If you're reusing those monkeys, cut the figure in half.
And if you're really interested, you can get your own Shakespeare Monkey T-Shirt at the Daily Wisdom Store. It'll be awhile before I get the Phobia Shirt done, but it's coming.