Am I allowed to deploy the same kind of Support-Unit twice for one Platoon, for example two sniper teams or even two Nebelwerfers. Or just one of every kind?

As long as it follows the restrictions laid out in your platoon type you can select whatever support unit you choose. There is no restriction on picking multiples of the same type of support unit.

Great, thanks. So two Nebelwerfers it is. Muahaha!