Hey, i don't know exactly what do you mean by rules.. but the qualifying rounds at Wednesday are exactly that, top 8 teams go to quarter finals at saturday.
And GNW packs depend on your final result so yep pretty much just saturday's round.
Number of pack depends only on where you place on Saturday.
As for the quarterfinal match ups, lol ..... I took screenshots of all group stuff for over 2 months and tried to figure out, it's NOT by points/power/activity/group level/members/fields won/previous weeks placements, so i am 99% sure it's just random. I did notice that a lot of time we got first match on Sat with one of 2 groups we fought on Wed, but that could be just randomness still since i only had like 10 sample size.