How is the deck performing with that many ETB tapped lands? 7-8 ETB tapped is a lot. Would some Darksteel Citadel be better than the UB lands or Blinkmoths (until you can get Urza's Saga)? Then you still build affinity but get untapped mana.
4th Mox Opal seems good. Between 4 Petal + 4 Opal + 4 tapped UW land, that should be enough color fixing. 16 blue sources and 12 white sources without the UB land.
Instead of Memnite, if you have some open slots left, what about Vault Skirge? It costs 1 mana and carries Plating very well. It seems like your deck may need more in the 1-3 cmc range to bridge the gap to free Frogmites and Enforcers. Skirge does that a lot better than vanilla 1/1 Memnite.