Typically freeroll sites are harder to convert to real money players.
I have worked with several affiliates that have freeroll sites and what we sometimes do is start with a freeroll and then work our way up to tournaments with some sort of play requirement in order to get in. That weeds out freeroll hunters and helps you to generate real money players.
The one thing I think you will have to worry about with running freerolls, is all the people that work to find out the passwords for private freerolls and distribute them to their network of freeroll hunters. You will get unwanted guests.
Best of luck.
Mark