Loot and XP: Having thought about it, I'm not posting any.
You are about to embark on your final adventure, so book-keeping is a little pointless. So here's what we'll do: If you are within a few thousand xp of leveling, say 5k, then just level up. Otherwise stay put. Between the fights, traps, and story reward, 5k seems like a decent estimate.
Regarding treasure, it matters little. Any magic items I give you will be useless in the Outlands, so other than selling them at half value they have no purpose. Sure, I just gave you a big pile of treasure, but the only things worth buying are magic items, right? I mean, what the heck else do adventurers ever spend money on? And I usually award taxes in between chapters for being thoughtful Lords, so that's another big pile of gold.
So unless you have any particularly extravagant purchases planned, let's just say the Hell Minstrels' loot, combined with your tax revenue and own personal savings, will cover it. If you think you have something expensive enough you want that it will be an exception, ask me.
But since this is relevant (and the only magic that will reliably work in the Outlands), here is the Key of Water
Physical Description: a small four sided pyramid made entirely of Turquoise, about three inches on a side. The sloped sides have small grooves that may allow it to fit together with other similar shapes objects, to form a cube. The gem is sea green, and shiny enough that it always looks damp.
Cosmetic Effect: When in possession of this pyramid, the wielder's skin looks wet, their fingers and toes grow webs, and they spout gills on the sides of their neck.
* The bearer gains immunity to Cold, but vulnerability to Fire.
* The bearer gains +4 Constitution, as Water is the ultimate source of all life.
* The bearer gains a swim speed equal to their land speed, a +8 to swim checks, and the ability to breathe underwater.
* The bearer can take on an Amorphous Form (as the spell in Spell Compendium) at will.
* The Key acts as an antenna pulling in energy from the moisture in the air around it. Once per day this energy can be discharged as a Cone of Cold spell. The Key can be combined with other Keys to produce more powerful spells, also useable once per day. The caster level for these spells is equal to the user's HD, and whichever mental stat is highest determines saving throw DCs.
* Water + Life: Rain of Roses (From BoED)
* Water + Death: Slime Wave (From SpC)
* Water + Earth: Acid Fog
* Water + Air: Control Weather
* Water + Earth + Life: Rain of Black Roses (From BoED)
* Water + Earth + Death: Obediant Avalanche (From CD)
* Water + Air + Life: Stormrage (From CD)
* Water + Air + Death: Storm of Vengeance