I actually just did the calculations and you are right! Long Sword+2 Health Potions is higher DPS. I have updated my guide as such.

The reason I like going with the Crystalline Flask+ Vision Ward is so I can sustain through some damage in a hard lane, and I can counterward. It allows you to counterward and make sure your enemy doesnt ward. It makes it so your enemy cannot overextend and allows you to get CS better.

The start option with Dagger you added is quite weak because you even mentioned that you should buy Zeal last when building Triforce so the better offensive option would be Long Sword + 2 Health Potions. Besides, it's recommendable to select one normal Sight Ward + Health Potion instead of the Vision Ward with Crystalline Flask..

The tenacity from Zephyr and Mercury's Treads don't stack, but I did the calculations and you can get up to 40% tenacity from Ionian Fervor when 3 enemies are near, plus 15% from Tenacious , and 35% from Mercury's Treads or Zephyr.

Yeah, he mentioned in the notes that you can replace Mercury's Treads with Zephyr so you still have the 35% tenacity..

You can actually gain a lot of tenacity on irelia, and as far as I know you usually won't hit the cap. Not 100% sure of this though, I didn't do that much testing (even though I have an irelia guide myself haha). Double tenacity items don't work though.

I dunno but I guess that you cannot gain 90% tenacity but 75% or so..
You should rework your cheat sheet because the reader first looks at this. Clarify staring items like Crystalline Flask + Sight Ward + Health Potion or Doran's Shield + Health Potion and so on like what you prefer. Furthermore add something like "Core Items" and mention Trinity Force and the build path like Phage -> Sheen -> Zeal or Sheen -> Phage -> Zeal. Yoo mentioned Blade of the Ruined King an the guide itself but not in the chaet sheet you might think of adding it to a segemnt "Offensive Items" or so. I definitively miss Spirit Visage as an "Defensive Item" (a furthermore segment) because it's so strong atm.. :)

Good Luck!