I think there's definitely a lot of potential here, and I love the magic system. I don't it's too complex, per se, but I think the key will be being very selective about what to include explicitly. I know you talked about the magic system being on the level of basic arithmetic, but I think it might be more helpful to introduce the world/magic system through a character that is uninformed about how the whole thing works. it gives the audience something to latch onto and identify with, and it forces you to figure out what are the most essential parts.
You'll have to think through what someone totally new to your world, i.e. the reader, is confused about, and what questions they will ask. That will help you sift through things I think. For example, a newcomer might feel that the one-chance-to-ascend thing is unjust, but not ever think to ask about whether a 112-year-old ascendent lives to 120 or 122. It's such a great magic system, and I can't wait to see what you do with it! I don't know where you want to go storywise, or if you've even gotten there yet, but regardless, I'm on the edge of my seat.