There are way more than four costumes for Chii and Freya.
In both the series and the manga, the characters change clothes just like you and me. Add to that the numerous outfits drawn in the Chobits artbooks, promotional items, etc., and you have quite a variety of outfits to choose from.
The picture you're talking about is from one of the artbooks, I believe. I think it was used on a few other things as well. My memory is kind of hazy at the moment, but I think it or a version of it also appeared in the series in a flashback scene, but I don't really remember if this is the case.
Freya and Chii are pronounced just like they sound (fray-yuh) (chee), although in the non-translated anime a lot of the characters pronounce Freya as fur-ay-uh, but I think that has more to do with them trying to pronunce a Germanic name with a Japanese accent. The languages are very different from one another and both have sounds that won't be found in the other lanugage.
Finally, people have a lot of different ways of making the ears and hair spools. I myself used painted wooden spools for the hair spools and used clear plastic rubber bands beneath them to keep them from slipping. The ears I made out of different colored craft foam, a thin wire headband, and hot glue. Different people make them in different ways though. Some use vacuformed plastic, sculpy, or purchased them from other costumers. You can usually do a search on Ebay and find several people who are selling them.
Costumes for 2007: Ran (Texhnolyze), She-Ra (She-Ra: Princess of Power), Marie's Black Masquerade Gown (Sofia Coppola's Marie Antionette), EGA Plum Walking Suit (Original Design)
Cons for 2007: Katsucon (tentative), Animazement (tentative), MomoCon, Dragon*Con, Anime Weekend Atlanta