Just make sure you're aware that when you pick up the Orb of Zot, all the portals in the dungeon will close. Specifically, you won't be able to go back into Hell.
Personally, I'd clear out Elf for the loot. Take it really slow. All of the Elves in Elf:7 are very dangerous. Bring a source of Warding and as much resistance as you can get spread out fairly evenly. If things start to go South because of the summons, flee. After that, I'd take on Shoals. Shoals is easier than Elf, but I've died so often in Shoals it's gotten me paranoid. After that, I'd suck it up and clear out Slime. Skip Tomb. The loot's good, but the rotting damage is crazy. It's a good use of all those otherwise useless potions of healing, I guess, but still. All the Torment and Smiting and Sphinxes and rotting and shit, it's just not fun. After that, I'd probably do Dis. Dis'll be pretty easy with a +9 eveningstar of holy wrath with high M+F skill. Then Cocytus if I had rC+++, then Gehenna if I had rF+++, then Tartarus if I had rN+++. At some point in all that (likely in Elf), I'd of gotten banished, so I'd scum the Abyss until I found the Abyssal Rune.
Conservation only saves items from flat out destruction. Pretty sure it has no effect on corrosion. Remember, artifacts and +5 items are immune to corrosion. Dwarven items and crystal plate mail don't get corroded 4/5ths of the time. rCorr saves 9/10ths of the time. +4 saves 98% of the time. All of these stack. And if you worship Jivya, you're free to loot Slime:6 at your leisure.
In fact, since Okawaru's wrath is ridiculously wimpy, strongly consider ditching him now that's he's given you a bunch of weapons and armor. If you've got good armor in all your slots and a good main weapon (hint: you do), you're not missing out on much. Might and Haste are useful, but TSO is more useful. If you start with Zin, you can waltz into Tomb, take a bunch of rotting damage, then cure it with vitrolization and cure all your mutations before ditching him for TSO or Elyvion. If you don't need mutations cured, just skip right to worhipping TSO, then liberally spam Daevas in Tomb. Sure, you'll lose a bunch of piety for spamming them, but you gain a bunch of piety for killing Mummies and the demons they'll summon. You will take some rotting damage, but it's not like your potions of healing are useful for anything else. If you need more good god piety, just go to the Abyss and walk around eating food and killing demons.