No, you're doing right for a BMW. "Heel and Toe" literally goes back to the days when the brake pedal was fairly far away from the accelerator and the accelerator was hinged on the floor (how many of you actually drove a car like THAT? hehe). Toes on the gas, heel on the brake. In some vehicles it was the opposite - the top of the accelerator was below the brake, so it was heel on the gas, toe on the brake. That was the harder way to do it. Now the pedals are generally much closer together.
I've been doing it since I learned to drive stick in a 1966 Ford "3 on the Tree" pickup when I was a teen on the mid '70s. I learned the concept and need for it (downshift & rev) when I started riding motorcycles at 14, so when I started driving a truck, I just did it, I thought it was what you HAD to do. I didn't know it was called "Heel and Toe" until a few years later.
As far as left foot braking, high school drivers training taught me NEVER to left foot brake, keep the left foot for the clutch. Now that I Autocross, I am trying to UNLEARN that and use left foot braking. There are some instances in autocross/racing where left foot braking is useful, such as trail braking into a corner and still keeping the engine revs up.