How much work to make multi-user blog, with ratings

(Not very familiar with Drupal)

I'm looking for software that will allow me to create a multi-user blogging system for a community of people. I'd like anyone to be able to sign up for an account, and create their own blog. I'd want some sort of approval process on their first blog post to make sure that they are worthy of having a blog, and that they are not just spammers. Either this way, or else a person must request that they be given a blog, and I'd click on something to make it happen if I approved them. I don't know which way is easier in Drupal.

I'd like registered users to be able to write comments on the blogs, and to rate the blog and the blog article itself.

As for the home page (portal?) I'd like to see an aggregation of the most recent blog articles from the community--actually excerpts would be best if I could, in reverse chronological order.

In the sidebar, I'd like to be able to select:

Blogs by rating
Blog article titles by rating
Blog article title by number of comments
Blogs article title by category

Of course each of these would have a link to the blog.

I'm sure there are things I'm not mentioning like ability to add banner ads, text ads, profiles for users, etc. But I think I've got the central theme down.

I think a standard template theme would work pretty well to start and I could customize it later.

So, my question, is, how difficult it something like this to pull off? I'd likely hire someone here to set it up for me, but what is the complexity level? I was reading a review of multi-user blogs today and it rated Drupla the highest for having what you need out of the box (not the ratings part).