Any thoughts?
We fundamentally have a Favored Soul & Sorcerer for a party commit so far and you're fundamentally thinking Monk which should work out pretty well.
I mostly want to go with
Xixecal out of your list. I'd take one Growth that way Eternal Glacier's 20% miss works against Mindflayer attacks and use the rest for more Ability increases (see faq) then remake up the damage loss using your 18th level Huge White Dragon mount that has 6th level Spells to kick out Greater Mighty Wallop. The reduced Size also avoids the Hide penalty, I'd grab a Collar of Greater Umbral Metamorphosis and a Wand or Child of Eberron pet up Camouflage for probably all the stealth you'd need. Remember, you have a free Blizzard following you around, anything further than 5ft away gains Concealment so while HiPS isn't a big concern the Hide bonuses are.
The Xixecal appears fairly defensive, DR 20, SR 40 (after vest), +20hp/rnd, immune to Cold/Fire (after mantle), and it's +20 Con. But it's also highly offensively it snags +20 Str before buffs, 4 Natural Weapons that all hit for +Slow & +1 Con dmg, you can also use your 2 Swift Actions to doublecast Cone of Cold for +40d6 more but it consumes 2 of your 6 uses. Recall the omgs over 50 Cha? Well that's a double edge because you'll easily break 54 Str (18 base, 20 class, 6 enhance, 5 level, 5 inherent) and your opponents will have a lot less than 50 Con. Hitting for probably 80 damage is enough to prompt a SoD whose DC is based off your Str and on failure utterly f'ing kills them so expect that to happen often and given that single target killing still has the excuse of "still weaker than our mage" you should have the goal of using it as often as you can.
Party wise the Xixecal offers no direct benefits as you'd expect out of the fighter guy but you do have a 12th level Sorcerer acting as your mount. Plus remember those blizzard rules I briefly touched on? You and you're allies are totally immune to it. So everyone else has a no-Save debuff of -4 Listen/Spot/Search & Ranged Weapon Attack rolls and the lovely mass Concealment debuff.
Feat Wise, since you'd be Large and your Dragon would be Huge you can ride it. Mounted Combat with a decent Ride Check could go along way to keeping it alive but don't forget to have it buff it's self. You're also a walking snowstorm vs 20th level casters in a campaign made by a guy whose homebrew hands out Resistance & FH/Regen like candy so take some abusive Metabreath Feats to compensate. A Two-Hander & Power Attack will make it pretty easy to hit KO ranges on your hulk smash (which has no size limitation) leaving the rest up for whatever. For your pet, I suggest the Snowcast line of Feats and focused on complimenting God style support.
