How many cfm do i need??

Check the cfm on the inline fan. Simply get a carbon filter that has a recommend cfm in your airflow range. If your inline fan blows 180 cfm, get a carbon scrubbe rated say ( 150-250 CFM) The setup of the 2 things does not matter as much but to let you know, I had cooler temps when air was pulled through the carbon filter by the inline fan.
Lemme know if you have an more questions or concerns =]