Gladiator goes to Paladin at 30 with a 15 (34 for stoneskin) Conjurer/white mage and uses Marauder for Mercy Stroke at 26.
Marauder goes to Warrior at 30, with a 15 Gladiator (22 Provoke, 34 Awareness) and Puglist 12 for Internal Release and Mantra at 42.
There is an additional Tank available after you've entered Ishgard in the Expansion Heavensward; called Dark Knight. It uses Marauder and Gladiator cross skills.


As to keybinds; its very personal preference how to set it up but I can list how I do mine as an example of needing keys taking a unique route. I've small hands so this is what I found works for me. Yes it looks like a mess, but if you need alot of bars and keys (which I could REALLY cut back alot on myself ;p) finding ways like this may help.

Bar 1] Keys 1-6, F, R, Shift+R, Alt+ 1-3 (alt 1-3 are on my mouse as well)
Bar 2] Keys Shift+1-6, Shift+F, G, Shift+G, Alt+ 4-6 (alt 4-6 are on my mouse as well)
Bar 3] Keys Alt+ NUMs 1-9 (While this is mostly used for my Mouse's "Shift" stance buttons, I also game Keyboard only a lot since the numpad can be used for targeting etc)
Bar 4] Keys Control+ 1-6 (on mouse, dont really use without because Control is awkward for my hands >.>) Rest are for clickable items which is mostly filled up with buffs/potions/etc
Bars +] I have 7-10 on the side, giving me quick click spots for minions, mounts, gear sets, Teleport/Return, and various other things like Gold Saucer, Challenge Log, Hud Layout, Waymarkers, Signs, etc. Also clickable Status Removal Potions.