Since the column of whitewash is so large, how can one stay under long enough to make it to the other end?

Yep, it is possible but takes lots of practice. You have to time the larger waves a little different than the small ones. If the wave already broke, get a good deep dive ahead of the whitewash. If the wave is going to break right in front of you, dive a little later than you would on a small wave. You need to dive right when the lip hits. Just keep adjusting your timing and you will figure how to push right through.
Aloha!

yes. It gets more difficult with colder water as it is more dense. Just duck dive deep and be pointing up when it hits you. You will break right through it if you are angled right. But if you are still pointing down early in the dive, it will rip you apart.

Yes.

it depends on many things, mostly on the type of wave and when it broke. if the wave breaks right in front of you it will probabaly pretty hard, but no its not impossible. if the wave is mush to begin with it will be a lot easier, bigger beach break or reef break waves will be harder.

yes, put your foot on the traction pad.

Yes its possible, but it takes practice. Even if you attempt a duck dive and fail on a big wave, its still better then turtelling or bailing.

At 10' there is a fair amount of luck involved. Obviously it is easier in warm water and without a wetsuit. It is also easier if you spend a lot of time in large surf practicing your technique. And then it depends on the wave. No one successfully duckdives 10' Pipe, but a good surfer could probably manage it consistently on a mushier wave.