creating a community with multisite and default blogs/profiles

hello together,

since weeks i’m trying find out the best solution for my requirements. i’m not sure if i really need Multisite.

My Requirements:

* Users can register and account is automatically activated

* Users can Post their favorite books to 2 Categories for example: “my favorite book” , “nice to have book”

* Users can see which books their friends posted (in activity stream)

* User A can See all Posts of user B by category in his blog/profile

* in this case the blog is more a profile as a blog (user can not create pages)

in my opinion i need multisite, but then i have the following problems:

* Blog must be automatically enabled after registering

* default theme and categories for new blog are set ” my favorite book”, ” nice to have book”

* users can not change the categories

* users have only frontent acces (no post edits in backend /wp-admin)

what do you think is the best solution for my requirements?

thanks in advance