As for a business plan there is always affiliate links to sites that sell the music/movies/etc like trueblueponies suggested, as well as ads. You can always think of a more exciting monetization strategy later, but the first trickle of cash would be enough to keep the interest going even it it may not amount to much.
This is the most reviewed album I found http://www.criticrania.com/content.php?type=music&id=30 Pink Floyd Dark Side of the Moon. It has only 6 ratings, yet is still a best selling album almost 40 years since it was released. Surely there could be more reviews and comments than that just from your social circle?
Never give up, never surrender. Never fool yourself either - if between you and your friends you can't write a dozen reviews[1] (or many more) for every album/book/whatever you like then maybe you don't have what it takes to make that site a success. There are always other ideas if this one doesn't work, just give it a fair shot.
1. maybe put links to reviews on other sites like Amazon, with an affiliate link. I am sure you could find many reviews of everything around the internet to link to, or to quote with attribution.