Hi! I think you kinda misunderstood that the point of THIS build was to build items that gave a combination of passive and active effects that contributed to soft CC. Iceborn Gauntlet is a core as is Rylais because their passives both slow, and allow Nami to capitalize (especially for those ranked lower) on her kit's natural hard CC. As I explained below, ruby sightstone gives an extra charge and 400 health, which both benefit Nami as she is naturally very squishy. While I understand that Mikhails is a good item, to me it is more situational, depending on the team, and I don't see a lot of actives put to great use in lower levels.

The ruby sightstone is good to get a little bit of extra health. Since (in bronze silver especially) having more survivability can literally make the difference between keeping you alive and dying in a fight, I appreciate the padding. Also, I find that the extra charge on the Ruby is good for chasing, as it allows you to check bushes without sticking your face in! :)

Greater Quints of gold might not be a must have, but they are good, in my opinion at lower elo, and also help make up any disparity in your ADC's ability to last hit, and the gold that would normally provide. They give a little bit of extra gold, and I find that extremely useful, but as I said in the section involving runes, they can be swapped if someone else wants to use something else instead :)

overall it's a decent guide but there really isn't a reason to rush for a Ruby Sightstone anymore since you can get all 3 wads off on the regular Sightstone. Also gold quints are no longer that great nor are they a must have.

It seems that you stuck a bit in Season 3 plays because Greater Quintessence of Gold aren't a big deal anymore and it's NOT mandatory to rush Ruby Sightstone because you would waste early gold you could use to buy more Mana Regeneration, Gold Regeneraition, Resistances or Ability Power in pure Health because a Sightstone already provides three wards. Iceborn Gauntlet and Rylai's Crystal Scepter a situational in my opinion and I question their use. I think you missed out Mikael's Blessing as a great option enabling Nami to spam more abilities due to huge Mana Regeneration and saving allies from crowd control/ over-time-damage etc..
For Masteries I just want to ofer you this, you might want to check it out: http://dpatti.com/s4/#dGvBQjsSAvA
For Coding and Guide writing I recommend you this one:
http://www.mobafire.com/league-of-legends/build/making-a-guide-101506