Facebook conundrum!

Hey All,
I have a site with approx 30,000 subscribers, there is a forum for the site too which has a further 15,000 users. I am currently investing approx €30,000 into the site for refurbishment and upgrade of certain functions (media driven stuff with lots of bespoke code). Here's my problem...

The plan is to do the work, prove our business model then acquire 250-500K venture capital for a complete rebuild and major marketing drive. I've already spoken to government funded enterprise boards and this is a runner if I can prove my strategy and meet the milestones. So I have to get this right!

Part of the rebuild will be a rebrand of the site and community to a new domain name. The new name is very recognisable and has global accessibility for the target market. Part of the long term strategy is taking advantage of traffic from Facebook (and other social networks). A Facebook page will be very important (we are currently running a beta test of the strategy on the existing name and the business model works).

The problem is, the vanity URL on Facebook for the new name has already been taken! If anyone here has any experience with generating serious traffic from Facebook I would love some input. Would a slight change between the vanity URL from the domain name be likely to cause a major issue (as a rule of thumb)? eg facebook.com/mysite not available so use facebook.com/mysitemedia (or some such extension). Branding and logos would all be the same. The domain name is so strong and so much of the concept and identity associated with the future of the business is hinged on it. What do you guys think?

I can't believe I overlooked the vanity url on facebook! If this is not a go then we will have to completely rethink our entire brand identity and elements of the business plan!