I think you should probably have the business cards made with a combination of roman letters and Japanese characters. Maybe something like this:-
Ｒａｌｆ－Ｐｅｔｅｒ Ｗｉｌｋｅ ラルフペーター・ヴィルケ
The company name is most prominent, then your job title, then your name. I used "shachou" for your job title: this means the man at the top (boss, chairman, proprietor). Your name should be written phonetically and, as your name is German and I'm English, I'm not sure I've got it right. What I have written is pronounced "Ralf Pay-tar Vill-keh" by an English person
The address will be in roman letters, although you could add ドイツ (Doitsu, or Germany) to make it clear where you are.
For the phone, e-mail, fax and so on I think I would use icons because everybody knows what they mean. That is, you would have something like this:-
☎ +49 (173) 5398 657
Hope this helps.