distance of light from ur plants depends on the type of light, type of fixture, and how old ur plants are. Its rare for me to disagree with @Seamaiden but i wouldnt practice "close as they tolerate". do research on what type of light ur using and see what others have done best with. i keep all HID fixtures 24"s + from canopy fwiw.
diy carbon filters will not work as well as a store bough filter. I use Phresh filters and have been very happy with them. If u plan to use a diy filter, make sure to pack the carbon as tight as it can and place in a mesh/micron bag before inserting it into ur "filter". the smaller the carbon, the better. oh and make sure to use active virgin carbon for its cleaner and will "scrub" the air better. I would place the filter in your grow area and have a fan recirculating the air through ur filter continuously. when air only passes through the carbon once, not all the "stinky air particles" will leach onto the carbon and u will risk smell being passed outside. much luck. Sküna