Well, you're not saying where you are getting your fresh air from, nor where it needs to exhaust.
Ventilation is pretty simple, it means moving air, you say you have an inline fan, how many CFM? calculate the cubic feet of your room and divide that by the CFM of your fan, and you have an idea how many air exchanges you are making. If you are using a passive exhaust (that means, just an exit, no blower fan), then it should be at least 3 times as large as the intake.