You might want to post a few reference photos, till then I can only give general advice.
As for hats, you have a few options. Alter and existing one, make a new one from scratch or commission one.
What ever you do use keep it light, your head will thank you at the end of the day. Model magic, fabric, and wire are a pretty good combo. Cardboard is also an option.
Naka-Kon '13- Steampunk, Princess Pluto (also helping make Mercury and Moon) Phoenix Ball gown.
Anime NebrasKon: Staff Shirt of AMAZING