newbie requires advice

hi guys,first time grower here,i have a small room,2.5 meters height,1 meter wide,2 meters long,i will have a 400 hps light in there,im hoping to grow 8 plants,i have very little funds and am wanting to keep costs down to a minimum,i have cut a ventillation grill in the entrence door,for fresh air access,i have cut a small hole in the back wall for exhaust,which im planing on fitting this fan http://www.diy.com/diy/jsp/bq/nav.j...refview=search&ts=1254642177316&isSearch=true
i will duct it through a charcoal cooker hood filter,i will be running a osillating fan on the light /plants,will this be ok for my ventilation needs?,also do i need to have the extractor on during the no light periods,thanks for reading