So would 2 or 3 pins per player be a good amount?
No. You want 12-15 per girl. In Salisbury the girls would exchange during opening ceremonies with girls from all over the place and all the age groups. Also ensure you get a lanyard or a towel so the girls can stick their new pins to them after trading and can hang it in their room with their trophies. What I noticed over the last 3 years is that you will never have too many pins to trade. Also ensure the manager has about 10 extra for the girls/teams that want a pin from the teams they play against. I always had 10 pins and would give 1 per game to the coach of the other team if they asked.