I don’t, but here’s a quick rundown of my thought process.
“Okay, hmm, what kind of character do I want to create. Well, I want them to be an Allomancer or Feruchemist, because I like those magic systems. Maybe both? What about a compounder? I like gold compounding, Miles Hundredlives was a great character. Gold compounding is cool, such an interesting form of immortality. Hey, maybe I should figure out a way do make some sort of immortality character. I’ve been listening to the musical Tuck Everlasting a lot recently and they have an interesting kind of immortality. How can I recreate that kind of immortality as a character? Let’s see, they wouldn’t age, and can’t die from any wounds. Gold and Atium compounding? Nonono, that’s way to OP. I don’t want them to be able to burn Atium anyway. Maybe to balance the OPness I have them not fight people. Like they actually don’t have the capacity to fight people, maybe they’re just unskilled in combat. Well, let’s figure out how to make them immortal later, how would I make this character interesting? I want them to be really really old. They could be lonely, as everyone they know died ages ago. Depressed, doesn’t make connections well. That could be interesting. What about the physical immortality, how do I make that interesting? I think the Gold compounding could result in some comical interactions, like they get stabbed and don't care, or fall from really high and walk it off. So I do want them to be comical, a funny character. But, I also want them to be really ancient. So, a humorous character on the outside, but lonely, wise, sad, and ancient on the inside. Also, Non-combative to offset the OPness of immortality. Wait a second.....”