Altering XP for Rappan Athuk

I just got a copy of RA for Pathfinder, and I've gotten my group fairly excited about playing around with an old-school meat grinder of a megadungeon. I definitely want to up the old-school feel of the module, but I also want to deal with the lethality by giving the players plenty of back-up characters so no one is stuck at the table without playing for too long. To that effect, I'm planning on implementing some XP adjustments and house rules to (hopefully) achieve these goals. I thought it would be a good idea to outline these ideas here to see if I'm completely barking up the wrong tree.

First, back up characters: I plan on using a variation on a rule that comes from the Dark Sun campaign setting. Basically, each player has a stable of 4 characters each starting at 1st level. Only one character is active at any given time, and that character earns XP normally. However, whenever the active character goes up a level, the player gets to level up one of his other three characters automatically putting that character's XP to the minimum amount to get them to the new level. These back up characters can be subbed in either when the party is back at town (at which point the currently active character gets put into the stable with the two remaining back-ups), or if a character dies one of the back-ups can be dropped in with some hastily constructed DM Fiat ("Wow, we're sure lucky you happened to be in this part of the dungeon - let's try to get out of here!"). If a character is subbed in after a PC death, the player makes a new 1st level character to add to their stable. I'm not sure how to handle equiping the back-ups - I could just say typical WBL until they're played and once they hit the "real world" they lock in their equipment and from there it's whatever they have or loot.

Second, treasure for XP: I'm thinking about adjusting XP from killing stuff down and adding XP from treasure to increase the motivation of exploration and clever problem solving. My basic thought is axing all XP from wandering monsters (that makes them resource sinks with basically no reward, so stealth and speed are important), and only granting 1/10th the noted XP value for "laired" monsters. Any treasure the party finds that's just worth money (coins, gems, art objects, etc.) would grant XP in a 1 GP of value = 1 XP awarded ratio. I think equipment and magic items will not grant XP as those are fundamentally useful and make the PCs more powerful (I am considering giving them 1/10th XP for sold items, but even at that reduction one powerful magic item could really skew the curve, I think). I haven't really dug into the amount of treasure available in the dungeon to know if this will keep them moving up the power level at a reasonable rate, but I am definitely digging the basic idea behind it. And it's not like Rappan Athuk is known for it's balanced encounter design in the first place.

Third, character advancment: I have gamed through several scenarios using the above ideas, and I realized there is a potential problem - wildly disparate party levels. In 3.5 there was the built in mechanic of lower level characters getting more XP for the same enounter. The math was cumbersome and it took longer than I liked to calculate (though a spreadsheet I finally made helped). That said, the built in catch-up mechanic was nice for this sort of situation. I do think that it is possible to replicate something like this using Pathfinder. My idea is setting the basic advancement to the Medium XP track. Any active character that is more than one level below the Average Party Level would use the Fast track, and any active character more than one level above the APL would use the Slow track. That should help pull up any lower level replacements while slowing down any higher level PCs. Once all the characters are back to parity, then everyone would be back on the Medium track.

Sorry for the wall of text; I appreciate anyone who has read this far. I'd like to hear any feedback regarding these basic ideas - do you think they will game out like I intend, or have I laid traps for myself.