milosevic - 2:17 am on May 26, 2012 (gmt 0)
How many visitors does the site get currently?
The best plan for me if you have to change the sites focus would be to replace the current content with informational content that's relevant to your project and keyphrases you will be targeting as soon as possible. Then bolt the commercial component on later.
Don't expect current backlinks to the site to count for much after you change it's purpose and topic though, and they could potentially hold the site back in establishing relevancy for something different.