Bearing in mind that in Pasuk 4, the Torah mentioned the Choshen before the Eifod, why here, does it mention the Eifod first?
Oznayim la'Torah: Because, even though the Kedushah of the Choshen exceeded that of the Eifod, it was not usable without the Eifod, since it was by means of the straps of the Eifod that it was attached to the Kohen Gadol's body.
How did they obtain the gold threads?
Rashi and Ramban (Sh'mos 39:3): They beat flat sheets of gold and cut them into thin strips. 1
How were the multicolored threads for the Choshen and the Eifod made?
Rashi: They spun one golden thread with six threads of Techeiles wool, with six threads of purple wool, with six threads of scarlet wool (all spun), and with six threads of twined linen, 1 before spinning them altogether - so that each thread comprised twenty-eight threads.
As the Pasuk describes in Sh'mos 39:3 (Rashi).
Only the Kohen Gadol wears the Efod, and it was of gold, three colors of wool, and linen. Why were 85 Kohanim called "Nosei Efod Bod" (Shmuel 1:22:18)? Also, "Bod" implies totally of linen!
Moshav Zekenim: Perhaps also Bigdei Kohen Hedyot are called Efod; it is an expression of an ornament.
Radak and Abarvenel (Shmuel 1:22:18): Targum Yonason there says 'proper to wear a linen Efod.' Great Ovdei Hashem wore it, e.g. David (Shmuel 2:6:14) and Shmuel (1:2:18). It was not a garment of Kehunah. 1