Is there a language requirement?
No and yes. We haven't specified that blogs must be in English, but please bear in mind that most people taking part are English speakers - answers to the questionnaire should be posted in English, and if your blog isn't an English Language one then ideally it'll be in a language that Google can translate, or put the Babel Fish Translator on your blog, so that your treater can find out a bit about you and the things that you like.
You'll also need to think about this when buying a magazine for the person that you're treating - the popularity of Japanese craft books with non-Japanese speakers shows that written language isn't always an issue - it's just something to think about.
If you would like to receive magazines like that, where you just want to ogle over the pictures and try and work out patterns yourself, please say so in your questionnaire when you fill it out.
When you are filling out your questionnaire, you should put as much information as you can into it, as this exchange doesn't require people to email each other to ask questions if they are a bit stuck on ideas and such-like. (Of course, you can always ask your treatee if you're not sure about something and they haven't mentioned it in their questionnaire)