The answer is not that simple. Technically yes you should be brake or accel only, and learn how to trail brake into a corner (google it lol).
But with some cars if you are skilled enough you can increase corner speed by controlling car balance modulating both pedals through the corner. This is pretty advanced though.
Also I would generally not recommend using left foot for brake / right foot for accelerator, especially do not do this on the road. Firstly I'm pretty sure it is illegal (and for very good reason), secondly if you are ever in an emergency brake situation, subconsciously you will plant both feet to the floor, hitting both the accelerator and the brake. Very dangerous and hence why it is illegal to drive this way on the road, even with an auto. I have known people who have nearly killed themselves doing this!
The generally recommended and most widely used method is heel toe. Only very limited drivers carry on use of left foot / right foot from their karting days (Greg Murphy is a case in point).
As for what gear to be in, you really don't want to be dropping your revs below around 4K in the FTO at the track.
Sorry haven't had time to look at the vids

I'm sure you had fun though
