I'm having a little trouble determining exactly what your problem is, but I will hit your list:
- I believe without exploiting potions and recursion stat boosting, the maximum percentage of magic reduction on a single enchantment is 25%. This is with 100 Enchant, 5/5 enchant stat, and the various corresponding element/weapon perks.
- Magnitude is not affected by armor type.
- You should be able to smith and enchant Dragon Scale Armor with 100% Destruction magicka reduction(free cast). Additionally, with the extra enchant perk, you could boost other school's cast regen, or eliminate it completely.
Remember you get the maximum enchantment power when using Grand or Black soul gems.
Never add/remove mods from a game in progress. Modding in skyrim is a bit buggy, and removing/adding mods during gameplay fucks up a lot of the scripts that run in the background.
So if you add mod, start over from the beginning. If you remove one, do the same.
Yes, this is very annoying. But sadly that is the only way to keep your games from not being corrupted.
But the important lesson. NEVER add or remove mods to a running game. (as far as I heard it still can crash even with all the additional tools and steps. It is best to not change mods, to keep your save clean).
Call Odahviing to Dragonsreach
First of all, I don't think this is a quest item. I think you mean this as a step in the fallen quest. If this is what you mean.
You could try to use console commands to force the quest to the next step. Look at the quest stages and advance the quest to the last one. You will miss out on some stuff, like the dialogue, and there is a chance that the next quest does not activate properly. But this is what you could try.
Disk space
One possible problem for save corruption is running out of diskspace during playing. Happened to me once. So make sure you have enough space on the disk where the saves get stored. (Default is your 'My games' directory).
Related question
This question has been asked before, see : how-to-fix-corrupted-save-files-in-skyrim
Teleport command
See this question: What is the proper teleport command in Skyrim?
Best Answer
Dunno if you found what you were after, but Lantern Oil is crafted at cooking spits in taverns or anywhere else that has a cooking spit. The conversion rate is 4:1 fat to oil.