I love this idea, but perhaps instead of making craftable elixirs there could be a separate alchemy component to the game? I love all of these activities, and I do agree that if elixirs are made 'craftable' they must be very expensive for the sake of KI keeping a good profit coming in for new additions to the game. If there is some type of alchemy addition to the game, there should be no recipes, only yourself choosing what to add to a potion to get some type of output, thus creating your own savable recipes. Of course, you could possibly have some sort of recipe vendor like a jewel recipe vendor that gives you a random recipe for the possible cost of crowns. Either way, I think making your own elixirs would be very cool.
Crafting elixirs would be really nice. I think that all of the elixirs should be craftable. For people who don't purchase crowns it'd be a nice change. Craftable elixirs would make pet making way less tedious.