Servus Mate!
Well, U can train them hiwever U want. Although I would recommend to let them grow a bit taller. It's rasiert to handle them when they, at least have 20cm in height. For a Rookie in terms of Training I'd suggest LST. You might wanna have a Look at my Mamba Negra Diary. There U see some nice Pics on how I did bend the plant. If you want to go for topping, wait until the 4th, or 5th node appear! The Plants should have a root-ball big enough to survive this technique. If u Cut them earlier you risk that the plant get's stunned.
Hope this helps a bit, good Luck! Servus, Oim.