I think it would depend on what someone wanted...since one really good and detailed piece might be worth 3-4 smaller piece. Maybe you should have catagories like small, medium, and large per the guidelines and let people choose or you could just decide that this should be a small/medium trade and let swap partners work out if they want to upgrade for a large. Anyhow you get to make the rules.
I have worked up a nice felt breakfast set: eggs, sausages, toast and I could totally see that you might want several sets of these to have enough play food, so I'd have no problem doing that.
You can see some of what I've made before in my profile. I hope some crocheters/knitters join because I'm really looking for that kind of food.