I know that any race that can play a warrior
can play it just fine.

What I'm wondering is if the big guys have
any advantage over the little guys (or medium)

The big guys get slam, and Ogre's are immune to stun
at least in the form of slam or bash.
Please correct me if I am wrong.
Trolls and Iksars get regen, yada yada.

Are these factors at later or even mid-levels or do the casters
pretty much handle the stun/interrupts on mobs?
I imagine they do, but
a little advice from the veterans would be appreciated.

I've never played a tank past 30 so I don't really know
the finer points. I loved playing a warrior, I just got tired of playing
him on PvP.

Is the Ikky bonus enough to make up for not wearing plate armor?
(which I didn't know about, thx.)

Or is there good enough gear for Iks so that it doesn't
matter that Iks don't get plate.

By what I've seen in EQ things like that balance later on.
I like platemail too much to consider playing Iks myself.
But I always think its good to know whats out there.

I don't know how much extra the AC bonus is for Iksar at higher levels but I imagine it is not very noticable on high end tanks with equal gear and AA. I think the plate armor restriction for Iksar was largely done away with over the years. New armor is usable by them for the most part, mostly only some of the older gear from that era should be limited now.

Overall by tankishness I would guess Ogre have the edge with the front stun immunity + Slam.

Iksar get to Forage, start with higher swimming skill, ac bonus and get bonus hp regen.

Wood Elves get Forage.

Trolls get bonus hp regen and can Slam.

Barbarians can Slam.

Frogloks have Ultravision, high swimming skill, better lung capacity, start with the most languages.

Gnomes can Tinker, never need a shrink.

Halflings get innate Hide and Sneak abilities which can help with some quests and selling to merchants.

Personally I'd choose either Ogre or Gnome. Ogre for the beefiness, gnome because I like tradeskills.