extraction is to remove stale air and replace with c02 rich(normal) air

a few fans moving air about will neither bring in c02, or bring down the temps created by running lights in an enclosed area......
they are required to move air around but its well down the list after....
work out your required amount of smoke needed(i go for 1 0z per week, per 12 week period)
ask yourself what kinda effect you like from your smoke, high or heavy, buzzing or blasted? have you smoked a type of weed that blew you away that you`d like to grow?
decide what growing medium youd like to use(hydro+ fast but tricky for newbs, soil = slower growth but much more forgiving).
work out the size of room you`ll need to grow that amount of weed.
work out your extraction and lighting requirements for the size of area.(ideally 50watts per sq ft and you`ll be looking to completely replace the air in your grow area every 3 mins/ both are optimum levels) you should note that the 2 (lights and extraction) are very closly linked.... big lights = high temp.
that should be something to think about m8, anymore q`s just ask