google hydroponics and see if any shops are near your area. You would be surprised to learn just how many hydroponic supply houses there are. Sometimes head shops sell nutrients but not very much and way over priced. Online shops exist too.

The second question is simple. Start flowering your plants when they are exactly half the size you want them to end up being. If you want a 4' plant, start flowering when the tree gets to be about 2' tall. In general under ideal circumstances, this will take about 6 weeks from seed or 4 weeks from a rooted clone state of a bout 2 or 3" tall. To be honest you can trigger flowering just about at any point past maturity. You will know your plant is mature when the branches that grow opposite from each other are no longer even. When the the branches start to grow staggered then from that point forward you can start flowering 12/12.