Aye, but stone fits thematically.
Also, I would have a Strength of 44 before magic items. I can make the Strength check. Usually. But in any case, I don't know how much of a benefit Mithral would be(I suppose it could get me another +2 to AC from Dex, though) versus other things.
Possibly not a Crusader; a Paladin/Cavalier or Paladin/Ranger(or all three) mounted charger would be hilariously ridiculous; thanks to my sheer power, I would function on land, too. The question is what sort of mount to use and how to acquire it. And whether I would be able to.
On the mounts; it looks like the only things big enough are Dragons (Which actually have mount rules, and never once says they cost more for having an older dragon) And Scorpions/Spiders (You have to use colossal though- something about riding too low, so you have to use an extra size bigger.. Don't worry, they come in colossal too.-also, it states a price for egg/training, but it never says that it costs any more for a bigger one

.. 2000 GP for a Colossal Spider Mount? Sounds fair to me) You could also theoretically use a soarwhale (Colossal size, and only 20' flying speed, but hey- It's a giant friggin' whale, what do you expect?), but I'm not finding much else (Arms and Equipment Guide for the Win!)
EDIT: Just realized that two of our backups are just big, strong, incredibly strong "Monsters"... I feel like our first roll is all going to be ranged glass cannons, and our second roll is going to be all incredibly strong melees/War hulks.