Is Sazh, a couple Shine's, and a Noctis into the cookpot the ideal route to evasion tanking? I'm also torn over going for a Ribbon or Discernment for my status prevention.
2x Noctis TM is the best for evasion tanking, but Noctis + Sazh TM is 2nd best. Keep in mind that the dodge from Noctis TM does stack, but the dodge from Sazh TM does not stack with itself, so don't farm more than 1 Sazh TM. For the remaining dodge to reach 100%, it depends on the unit.
If they can wear Light Armor, then Assassin Vest for the chest is the best option (trial reward). If they can't wear light armor, but can wear clothes, Vampire Cloak is the best chest, but it's a 5* TM from a limited time banner (Dracula Lasswell, on Halloween banner part2). I wouldn't advise anyone to chase Dracu Lasswell though unless you're a millionaire since his banner is bad and so is the unit besides the TM.
Using materia slots to get he last % is a good idea, using Shine, Yda, or Cyan's TM (Yda's is limit:1, the others stack). You can also get some from weapon slot (10% katana, 5% dagger), heavy shield slot (5%), or hat slot (5%).
For Ribbon or Discernment, the answer is get both. You eventually want 5 copies of full status immunity for your team. I personally went with 3 ribbons and 2 discernment, and it's worked out well. Do at least 2 and 2, then it's really not much difference which for the 5th.