Developing my reading comprehension?

Please look at the following article.

Carlos was perfect as a teacher. He took personal interest in those with whom he had to deal, and knew both their strong and weak points.
He would elicit from a pupil the best of which a pupil was capable.
In all the young men with whom he came in contact he inspired a real and lasting affection.

-In fact, it was a little difficult for me to understand all of the sentences.
[Q1] What part of speech "the best of which a pupil was capable" is? I think it is adverbial phrase.

[Q2] Can I rewrite "In all the young men with whom he came in contact" to " In all the young men he contacted with"

This phrase is so difficult for me to recognize its meaning. I think "whom" indicates "all the young men". Could you explain to me its meaning more clearly?

Thank you for your answer in advance.