Welcome, Gabby!
🙂
All I can really say about figuring out what to collect is that it takes time to learn what is most important to you, and your tastes will probably change here and there, so don't worry too much about what you want to "mainly" collect right away! You can always use your old pins as traders if you end up not wanting them anymore!
I would say think about your favorite movies, attractions and characters, and start there. Over time you may find that you really only like a certain scene or character from that movie, and can trade away the pins you have that aren't specific enough. Or maybe you will find that you have a thing for characters dressed as other characters, or maybe a certain holiday, the black & white classics, balloons, food - who knows! You might be surprised what attracts you when looking at all of the pins online, and suddenly a new collection will start to grow!
Just have fun with it!
I don't live near any parks, so I can't really help with that, but for more options I know a lot of good honest members here sell pins in the "Pins for Sale/Wanted" section. Sometimes there will be a large sale while someone is trying to get rid of all of their traders (or they quit the hobby and are selling everything), so prices may be less than eBay, etc..