Some of these details are still subject to change as they are tested and we receive feedback on them.
Favour costs are primarily balanced around what tier of item it is. So a unique item with 3LP will have a higher favour cost than a magic item.
We pretty intentionally left off specifics of what each prophecy does. I think you’re thinking about the right sort of thing but not likely to be able to say “I want this specific item with these specific stats dropped from this specific person”. More along the lines of things similar to “the next unique that drops is guaranteed to have LP” or something kinda like that ish.
As for Bazaar search/sort, it will be very powerful and very low friction.