Interactive Website - repost

Start-up, web-based company needs help with website development of a site meant for children. Graphics and content are not an issue for us. Our challenges are in making the site interactive with its visitors. Here are some examples of what we'd like to accomplish from a structural standpoint: 1) Require log-in for user identity. Usernames and passwords given after nominal fee. Only logged in users would be able to use everything on the site 2) Allow logged in users to post comments, possibly with comments screened before posting 3) Enable each user to maintain a personal diary on the site, visible only to that user (or his parents who have special log-in). 4) Enable users to become "friends" with other users in a kind of Facebook format. 5) Enable users to submit videos of their own experiences. 6) Enable users to compare and vote on posted videos. There could be more than this, but for now, I'd like to get an idea of who can do these things and how they would charge. I've placed a price range on the project. If it's too much, or not enough, please let us know.