Hello there Roy, some days ago played one 10 mBTC freeroll and as someone already told starting stack, in terms of BB, make the tournament a lottery meaning that you have to gamble away to build a nice stack at the beginning otherwise you just get blinded out in matter of few rounds also considering it's a six handed format if I recall correctly.

In my opinion it would be preferable splitting this 10 mBtc in more tournaments: maybe ten 1 mBTC freerolls one every couple of hours or so,  to cover most of timezones and to have some action running 24h on site.
Maybe add some rake requirements to withdraw freeroll winnings or viceversa add rake/raked hands requirements to join freerolls so to have also cash tables running ... I have lot of ways in mind to try rising traffic a bit up but then it's up to you evaluating if they are a sustainable business.