Bracing is going to depend on your soil and what technique you want to use. I use 2.5 meter posts sunk about 1 meter into the ground then concreted, on the inside of the angle I have a brace post that is also concrete. There are other ways to brace corners with and without concrete. Just google High tension cable fence installation.
T posts are green steel posts with a "T" shaped cross section. Lots of fenceing assesories are made for them. They are driven in the ground with a tpost driver. Properly installed HT cable is perfectly safe. Problems arise when people use weaker softer wire and call it HT cable when it isnt. Or it isnt properly installed.