Servus Mate!
Well, you can train them however you want. Although I would recommend letting them grow a bit taller. It's easier to handle them when they have at least 20cm in height. For a rookie in terms of training, I'd suggest LST. You might want to have a look at my Mamba Negra Diary. There you see some nice pics on how I bent the plant. If you want to go for topping, wait until the 4th or 5th node appears! The plants should have a root ball big enough to survive this technique. If you cut them earlier, you risk the plant getting stunned.
Hope this helps a bit, good luck! Servus, Oim.