Quote from JujuCalibretto is exactly right. To elaborate, in pauper, the amount and quality of mana fixing across the colour combinations is very limited. Using up to 7 (!) multicolour cards of each combo is definitely a bit much.
I have a 405 card cube myself. I run 4 cards of each 2 colour combination, and even then I think that's too high. I'm going to be expanding to 450 cards eventually, and I don't think I'll be adding any more multicolour cards.
Quote from LanxalWell, on Wrecking Ball, if I was to include it, what would you cut? I like all four of the current RB cards.
Quote from calibrettoUpgrades all around, IMO. Great update, man!