What purpose did the Paroches serve?
Rashi, Ramban (Pasuk 33,34), Seforno and Targum Yonasan: The Paroches served to divide the Kodesh and the Kodesh Kodshim, where the Shechinah resided. 1
Which the Chachamim (in B'rachos, 18b) call 'Pargod' (See also Targum Yonasan) - something that divides between the king and the people (Rashi). The division was total, inasmuch as one half of the bottom curtains (the 'Mishkan') covered the Heichal; the other half, the Kodesh Kodshim, as Pasuk 33 indicates (Rashi [Refer also to 26:4:1:1*]).
How thick was each of the respective threads?
Rashi: Each completed thread comprised each of the four individual threads (linen, dark blue wool, purple wool and bright red wool), each of which had been spun into a six-fold thread. 1
What is "Ma'aseh Choshev"?
Rashi and Rashbam: Refer to 26:1:3:1.