Moving Categories into sub-domains

Hi. So I am trying to create sub-domains according to some of the more popular categories on my site. I have the 3 following requirements:

1) Each category url should be category1.example.com instead of example.com/category (yes pretty URLs are working on my site).
2) Each sub-domain can have different themes and styles.
3) I want to add posts to my main blog, and categorize it and it should automatically be added to the sub-domain.

I have read a lot of multi-site, but I am not sure if thats the solution here, because I think that is inherently creating new blogs which would need to be maintained seperately