1) Can someone name the most important commentaries, sub-commentaries, etc. I should read while reading the Tipitaka?
There are no important commentaries & sub-commentaries. The Buddha did not teach his Dhamma for there to be a necessity for commentaries & sub-commentaries. Commentaries are heretical to what the Buddha taught. If you place faith in commentaries & sub-commentaries then you do not have faith in the Buddha & the Dhamma. Instead, you have faith in other individuals, who often misunderstood the Dhamma. The Buddha taught:
The teaching is well explained by the Buddha—visible in the here & now, immediately effective, inviting inspection, relevant, so that sensible people can know it for themselves.
Monks, in this Teaching that is so well proclaimed by me and is plain, open, explicit and free of patchwork
Thus spoke the Venerable Ananda, but the Blessed One answered him, saying: "What more does the community of bhikkhus expect from me, Ananda? I have set forth the Dhamma without making any distinction of esoteric and exoteric doctrine; there is nothing, Ananda, with regard to the teachings that the Tathagata holds to the last with the closed fist of a teacher who keeps some things back.
In future time, there will be bhikkhus who will not listen to the utterance of such discourses which are words of the Tathāgata, profound, profound in meaning, leading beyond the world, connected with emptiness, they will not lend ear, they will not apply their mind on knowledge, they will not consider those teachings as to be taken up and mastered. On the contrary, they will listen to the utterance of such discourses which are literary compositions made by poets, witty words, witty letters, by people from outside [the Dhamma], or the words of disciples, they will lend ear, they will apply their mind on knowledge, they will consider those teachings as to be taken up and mastered. Thus, bhikkhus, the discourses which are words of the Tathāgata, profound, profound in meaning, leading beyond the world, connected with emptiness, will disappear.
However, if you are that keen:
In my opinion commentaries and sub commentaries are important. Even the Tipitaka is a tabulation by certain Arahants. In any case, I ask a similar question in the Dhamma Wheel.