How many suspects are too many?

I'm toying with the idea of a room filled with potential murderers. So far, I think it's working, but we'll see once an editor weighs in. Here's where I'm going: A horrible woman drops dead at her birthday party. At least 20 people at the party had motives to kill her. 

I think that as long as I eliminate most of the suspects before the reader becomes frustrated, I can pull this off. 

Wish me luck!