One of the least investment methods I know of is the K.I.S.S with Maxibloom (about $15). Generally this is used with COCO coir in a Hempy bucket but maybe you could adapt it to work with your setup? It would not be organic though...
http://forum.grasscity.com/coco-coir/966945-kiss-maxibloom.html
I have cooled a 400 watt light in a tube with a 4 inch fan before. Grab a little one and you will be fine. Especially if you are running a separate intake and exhaust.
I would say chemistry for sure because it will probably be required at any accredited school for a degree, that or biology. Take chemistry and biology intro level courses in the beginning. They will give you a good overall understanding of how anything "sciency" works. It will also give you time...