So I'm going to a convention for my very fist time and plan on being Amulet Dia from Shugo Chara. I see many other people simply put their hair up in pigtails other than buying the wig. should I just go as someone else?

I’m not sure why you would go as someone else because of how other people do their cosplay? If you’re asking if you should do a wig, I would say yes. I’m gonna make a big post in a few minutes about wigs, look for it.