Welcome to the world of pin trading!
It's up to you if you want to buy some before hand, but it's worthining thinking about it in terms of cost. You can often find pretty good deals for 'trader' pins on places like Dizpins Sale Board (Google for it). Otherwise you can find pins at WDW, but normally at a higher price (lowest are probably $6 or so).
Because you're going in 9 days, you might not have enough time to mail order the pins, but you could email the seller and ask.
A good place to start in
www.dizpins.com or
www.pinpics.com for info about pin trading.