In my recent past of running these things, we never had too many participants to worry about a cutoff as we did previously. I would not be concerned about it until you felt you were getting close to a number that you felt was not managable.
Also, I always suggested new cards, preferably the same, so it doesn't turn out to be just a way for folks to unload old mixed cards that have made the rounds on several occasions. I think that worked out better because when people commented about a card from somebody, everybody was on the same page as to who sent what. Less chance of disappointment if someone talked about getting card x, people get excited about what is coming, but they ended up getting card y.
