Offer a beta period as soon as you possibly can and give those profiles 'memberships' for 1-2 yrs free. Be honest with them and they will start filling it up. Then when you feel you have anough of a lead, add in the payment system (i'm assumming you are ultimately charging for the site) and you're done

That iMHO is far better than batch import or fake profiles...

Good luck with you vision!

Dave