What is the meaning of "Veshibatzta ha'Kesones Sheish"?
Rashi: 'And you shall make the tunic of linen in the form of (ornamental) settings.
Why does the Torah not inform us here what the belt was made of?
Ramban (in Pikudei, 39:29): The fact that the Torah describes the belt as "Ma'aseh Rokeim" indicates that it was made of the same materials as the screen of the Ohel Mo'ed, where the Torah uses the same expression, 1 and specifically writes that it was made of Techeiles, Argaman, Tola'as Shani and Sheish Moshzar. 2
What did the Mitznefes and the Avneit respectively, atone for?
See Peirush Yonasan.
Seeing as the Kohen Gadol put on the Avneit before the Mitznefes, why does the Torah mention the Mitznefes first?
Oznayim la'Torah: Bcause, as opposed to the Avneit, which was made Ma'aseh Rokeim, of twined linen, Techeiles and Tola'as Shani, 1 the Mitznefes was made of linen in exactly the same way as the Kutones, which the Torah mentioned just before it.
What are the specifications of the Mitznefes and the Avneit, which, for some reason, the Torah does not give?