2 kids 230 pins - the TSA loved us - we traded all week long. the thing to remember is that if you go down with 100 pins you will probably come home with 120-130 after purchasing pins in the park - it's really addicting and fun.
We have been trading a year now and I have about 900 pins - 500 or so are FIGMENT, 100 - 150 Mickey same for Tinker, 50 Halloween and 18 Hanukkahs - the hardest thing is deciding were to concentrate your trading!
We also have near 150 'traders' for cast lanyards so they add up pretty fast ;-)
Also - you should try to pick up cheaper trading quality cast lanyads type pins - do NOT trade a $6-$14 dollar pin for a cast lanyard or a cheap pin. We made that mistake the 1st year we went to WDW and a CM said - why not buy the starter sets where you get 6-8 pins for $30-35 (like $4-5 a pin) and save $. We had already spent a lot of $ on open rack pins we were trading for lanyard stuff - but we were totally new and had no clue.